This section has 4 verses.

 Titus 3:8-11
8 This is a faithful saying, and these things I will that thou affirm constantly, that they which have believed in God might be careful to maintain good works. These things are good and profitable unto men.
9 But avoid foolish questions, and genealogies, and contentions, and strivings about the law; for they are unprofitable and vain.
10 A man that is an heretick after the first and second admonition reject;
11 Knowing that he that is such is subverted, and sinneth, being condemned of himself.

We will begin with the Barclay commentary.

THE NECESSITY OF ACTION AND THE DANGER OF DISCUSSION

First, the paraphrase of verses 8-11:

This is a saying which we are bound to believe – and I want you to keep on affirming these things – that those who have put their faith in God must think and plan how to practice fine deeds. These are fine things and useful to men. But have nothing to do with foolish speculations and genealogies and contentious and legalistic battles, for they are no good to anyone and serve no useful purpose. Avoid a contentious and self-opinionated man, after giving him a first and a second warning, for you must be well aware that such a man is perverted and stands a self-condemned sinner.

THIS passage stresses the need for Christian action and the danger of a certain kind of discussion.

The word we have translated as to practice fine deeds is proistasthai, which literally means to stand in front of and was the word used for a shopkeeper standing in front of the shop and calling out to advertise the produce. The phrase may mean either of two things. It might be a command to Christians to engage only in respectable and useful trades.  There were certain professions which the early Church insisted that people should give up before they were allowed even to ask for membership. More probably, the phrase has the wider meaning that Christians must practice good deeds which are helpful to others.

The second part of the passage warns against useless discussions. The Greek philosophers spent their time on their over subtle [over-precise, picky, hair-splitting] problems. The Jewish Rabbis spent their time building up imaginary genealogies for the characters of the Old Testament. The Jewish scribes spent endless hours discussing what could and could not be done on the Sabbath, and what was and was not unclean. It has been said that there is a danger that people might think themselves religious because they discuss religious questions.  It is much easier to discuss theological questions than to be kind and considerate and helpful at home, or efficient and conscientious and honest at work. There is no virtue in sitting discussing deep theological questions when the simple tasks of the Christian life are waiting to be done. Such discussion can be nothing other than avoidance of Christian duties.

Paul was certain that the real task for Christians lay in Christian action. That is not to say that there is no place for Christian discussion; but the discussion which does not end in action is very largely wasted time.

It is Paul’s advice that contentious and self-opinionated people should be avoided. The Authorized Version calls that kind of person the heretic. The Greek is hairetikos. The verb hairein means to choose, and hairesis means a party, or a school or a sect. Originally, the word carried no bad meaning.  This creeps in when someone sets private opinion against all the teaching, the agreement and the tradition of the Church.  Heretics are simply people who have decided that they are right and everybody else is wrong. Paul’s warning is against those who have made their own ideas the test of all truth. We should always be very careful of any opinion which separates us from the fellowship of our fellow believers. True faith does not divide people; it unites them. ~Barclay Commentary

Note: Heretic

A professed believer who maintains religious opinions contrary to those accepted by his or her church or rejects doctrines prescribed by that church [from the Word of God].

Now to the other commentaries where we begin with the general and go to the specific.  First the Matthew Henry Main.  The commentary covers verses 9-15 but I will pick it up where it discusses verse 11

Knowing that he that is such is subverted (turned off from the foundation) and sinneth grievously, being self-condemned. Those who will not be reclaimed by admonitions, but are obstinate in their sins and errors, are subverted and self-condemned; they inflict that punishment upon themselves which the governors of the church should inflict upon them: they throw themselves out of the church, and throw off its communion, and so are self-condemned. Observe,

1. How great an evil real heresy is, not lightly therefore to be charged upon any, though greatly to be taken heed of by all. Such a one is subverted or perverted - a metaphor from a building so ruined as to render it difficult if not impossible to repair and raise it up again. Real heretics have seldom been recovered to the true faith: not so much defect of judgment, as perverseness of the will, being in the case, through pride, or ambition, or self-willedness, or covetousness, or such like corruption, which therefore must be taken heed of: “Be humble, love the truth and practice it, and damning heresy will be escaped.”

2. Pains and patience must be used about those that err most grievously. They are not easily and soon to be given up and cast off, but competent time and means must be tried for their recovery.

3. The church's means even with heretics are persuasive and rational. They must be admonished, instructed, and warned; so much nouthesia imports. We discussed this word, "nouthesia" at length in our discussion of verse 10.  Here is a brief reminder:

4. Upon continued obstinacy and irreclaimableness, the church has power, and is obliged, to preserve its own purity, by severing such a corrupt member which discipline may by God's blessing become effectual to reform the offender, or if not, it will leave him the more inexcusable in his condemnation.

Note: Nouthesia [item 3 above]:

From biblical times onward, God's people have counseled nouthetically. The word itself is biblical. The New Testament was written in Greek, from which the noun nouthesia (verb: noutheteo) comes. It is a term used largely by the apostle Paul which is sometimes translated “admonish, correct or instruct.”

It is Strong's word 3559. It gives the meaning as "a warning, admonition, counsel."

3559 nouthesía (a feminine noun derived from 3560 /nouthetéō) – properly, setting (placing) the mind through God-inspired warning ("admonition").

3559 /nouthesía ("warning through teaching") improves a person's reasoning so they can reach God's solution – i.e. by going through His thought-process. See 3560 (nouthetéō).

I looked up the phrase, "Nouthetic counseling" today, as this is something God's church has practiced from the beginning.

Nouthetic counseling (Greek: noutheteo, to admonish) is a form of Evangelical Protestant pastoral counseling based solely upon the Bible and focused on Christ. It repudiates mainstream psychology and psychiatry as humanistic, fundamentally opposed to Christianity, and radically secular. ~Wikipedia https://en.wikipedia.org/wiki/Nouthetic_counseling

I next went to the Institute for Nouthetic Studies to get their definition.  The question is, "What is Nouthetic Counseling?"  Here is their answer:

In introducing the subject, I have indicated that it is biblical counseling. That is the fact that I wish to affirm as stoutly as possible. Many people claim to do biblical counseling, but the claim must always be examined closely to see if it stands up under scrutiny. In most instances, it does not. The use of the Bible does not, in itself, validate the claim. How the Bible is used is of critical importance. If it is used merely to back or illustrate the principles and practices of a counseling system that has been borrowed from some non-Christian source or sources, then it certainly has no right to claim either the description Biblical or Christian. Just because a Christian does counseling, that does not mean that the counseling he does is Christian.

Christian (or biblical) counseling must be biblical throughout. That is to say, it must not merely use the Bible, it must be based upon and grow out of biblical teaching at every point. It must be a biblically-derived system. In other words, truly biblical counseling must be exegetically-founded. Its principles and practices must be mined from the Bible and be systematically self-consistent with it in every respect.

"But what of Nouthetic counseling?" you ask. All that I have just said is what Nouthetic counseling stands for. Doubtless, you would want that further explained. For instance, you might wonder why we don't simply call our counseling Biblical or Christian. Either name certainly is a viable option. But the problem is that because of all of the conflicting and confusing nomenclature abroad in the Christian church, it would identify virtually nothing. A name ought to help the one who reads it to distinguish it from others that might seem to be similar. Because there are so many who use the names Christian or Biblical, those names no longer distinguish any system from any other. The word Nouthetic, on the other hand, stands out from the pack. Because only those who want to be known as such will use the name, it separates the system from others and eliminates much confusion.

But you will want to know precisely what the word Nouthetic means and how it is I choose that name to describe the biblical system of counseling I espouse. The word comes from the Greek New Testament. It has, within it, three elements-concern, confrontation, and change. Nouthetic counseling is counseling that involves face to face confrontation by one person to another, out of loving concern for him, in order to bring about the changes God desires in his life. That in a nutshell, is what Nouthetic counseling is all about. ~Institute for Nouthetic Studies

So, this is a biblical word with a very specific biblical meaning.  We go now to the Biblical Illustrator and a piece we used in our discussion of verse 10:

An heretic … reject

The treatment of heresy

I. Heresy is not an unsound opinion, but an unsound life. A man may hold an erroneous opinion and hold it sincerely; but the word used here denotes one who seeks to promote discord in the Church (See Romans 16:17).

Quoted verse:
Romans 16:17
Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.

II. Heresy is to be dealt with firmly, but gently.

1. Firmly—by admonition.

2. Gently—by repeated admonitions.

III. Hardened heretics are to be rejected.

1. But this only applies to exclusion from Church fellowship.

2. It is no warrant for persecution.

3. Excluded heretics are to be deemed objects of pity. ~Biblical Illustrator

Here are three other pieces:

Treatment of heretics

Paul having exhorted Titus both to teach the truth according to godliness, as also to resist all such foolish and vain doctrine as might do hurt in the Church of God. Titus might object: This indeed is my duty wherein I extend to exercise myself with diligence; but when I have laboured and done all I can, many there are who will not yield to the truth, nor submit themselves to this ordinance of God; how am I to carry myself towards such? Answer: The apostle, careful to prevent all such things as he foresaw might be hurtful to the Church, giveth direction in these two verses how to proceed in this business also. The former, giving direction and laying down the duty; and the latter, enforcing the same by moment of reason. In the former are three things to be considered:

1. The persons against whom Titus is to deal—here called heretics.

2. The direction how he is to behave himself towards them—reject them.

3. The orderly manner of proceeding, after once or twice admonition.

The latter verse containeth the reason of this severity, because such persons are incurable and incorrigible; which is proved by two arguments.

1. Such a one is subverted, that is, turned or cast off the foundation.

2. He sinneth against his own conscience, being damned of his own self, that is, he wittingly and willingly spurneth against that truth of which his conscience is by the former admonition convinced. ~Biblical Illustrator

Heresy not to be trifled with

I am asked sometimes to read an heretical book. Well, if I believed my reading it would help its refutation and might be an assistance to others in keeping them out of error, I might do it as a hard matter of duty, but I shall not do it unless I see some good will come from it. I am not going to drag my spirit through a ditch for the sake of having it washed afterwards, for it is not my own. It may be that good medicine would restore me if I poisoned myself with putrid meat, but I am not going to try it: I dare not experiment on a mind which no longer belongs to me. There is a mother and a child, and the child has a book to play with, and a black lead pencil. It is making drawings and marks upon the book, and the mother takes no notice. It lays down one book and snatches another from the table, and at once the mother rises from her seat, and hurriedly takes the book away, saying: “No, my dear, you must not mark that, for it is not ours.” So with my mind, intellect, and spirit; if it belonged to me I might or might not play tomfool with it, and go to hear Socinians, Universalists, and suchlike preach; but as it is not my own, I will preserve it from such fooleries, and the pure word shall not be mingled with the errors of men. ~Biblical Illustrator

Contagion of false doctrine

Sin is like the bale of goods which came from the East to this city in the olden time, which brought the pest in it. Probably it was but a small bale, but yet it contained in it the deaths of hundreds of the inhabitants of London. In those days one piece of rag carried the infection into a whole town. So, if you permit one sin or false doctrine in a church knowingly and wittingly, none can tell the extent to which that evil may ultimately go. The Church, therefore, is to be purged of practical and doctrinal evil as diligently as possible That sour and corrupting thing which God abhors must be purged out, and it is to be the business of the Christian minister, and of all his fellow helpers, to keep the church free from it. ~Biblical Illustrator

Here is something I found in the Pulpit Bible commentary;

The right attitude of Christian ministers toward divisive errorists.

"A man that is an heretic after a first and second admonition avoid."

I. THE TRUE NATURE OF HIS OFFENSE.

1. It is not a case of fundamental or doctrinal error, such as the words "heretic" and "heresy" came to imply in after-ages. Yet it is a mistake to suppose that separatist ways are not caused by divergences of judgment on some points from the settled belief of the Christian community.

2. It was a case of a turbulent sectary, dissatisfied with the Church, who withdrew from her communion to the disturbance of her peace. He would try to justify his course by a difference of opinion upon matters of doctrine, worship, or organization.

II. THE METHOD OF DEALING WITH THE OFFENDER.

1. He was to receive two admonitions in succession. He was to be twice warned not to pursue his divisive courses; he was not to be contended with, but rebuke was to be employed to recover him from his error.

2. His pride or his ambition would not allow him to yield to admonition, he was to be, not excommunicated—the course adopted by the apostle himself in another case (1Timothy 1:20); but simply avoided. There must be no intercourse with him. This was a virtual excommunication, for he no longer held the place of a Christian brother.

Quoted verse:
1 Timothy 1:20 [see Lesson]
Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme.

III. THE JUSTIFICATION OF THIS METHOD. "Knowing that he that is such is perverted, and sinneth, being self-condemned." The case is an utterly hopeless one. You must have done with the divisive sectary; let him alone.

1. For he is perverted; implying an inward corruption of character, which steels him against all official admonition of the Church.

2. He sinneth. He errs knowingly, for his course has been authoritatively condemned by the messenger of God.

3. He is self-condemned. This does not mean that he consciously acts a part he knows to be wrong, but that he has condemned himself by his own practice, practically consenting by his separation that he is unworthy the fellowship of the Church, and thus justifying the Church in its rejection of him, or that he stands condemned by the Scriptures which he himself accepts as his rule of faith and life. ~The Pulpit Bible

Now to a specific commentary:

The verse is broken out in three parts:

1] Knowing that he that is such is subverted.
2] And sinneth.
3] Being condemned of himself

1] Knowing that he that is such is subverted.- Or overturned and demolished; he is like an edifice, that is not only decaying, and falling, but is entirely everted [turned inside out], and pulled down; so that there is no hopes of a restoration or recovery; he is in a desperate condition, having opposed the person, or office, or sacrifice of Christ; having either trodden the Son of God underfoot, or counted his blood common, or done despite unto the spirit of grace; in either of which cases there is no more sacrifice for sin: ~John Gill

2] And sinneth - not practically, but doctrinally, and willfully after he has received the knowledge of the truth; by denying the truth he received, in which he continues, notwithstanding the evidence of the word of God is against him; and; notwithstanding the arguments taken from it by the ministers of the Gospel, to convince him; and notwithstanding the admonitions of the church to recover him out of the snare of the devil: ~John Gill

3] Being condemned of himself - not that an heretic is one that is convinced in his own conscience that he is in an error, and that that is a truth which he opposes; and yet he obstinately persists in the one, and continues to set himself against the other; for then, none but an hypocrite, that conceals his true sentiment, can be an heretic; nor can any man be known to be one unless he accuses himself; since no man can know the heart of another; and it would be impracticable in a church to deal with heretics, or reject and excommunicate them: but either the meaning is, that he is such an one, who by his own practice has condemned himself; for whereas he has separated himself not only from the faith of the church, but from the church itself; by so doing he practically condemns himself, or judges himself unworthy of the communion of the church, and so justifies the church in their rejection and exclusion of him: or rather, an heretic is one who having professed Christianity, and received the Scriptures as the only rule of faith and practice, and still professes to abide by the same, and that all doctrine is to be tried by them, and to be approved or condemned as that agrees or disagrees with them, stands condemned by those Scriptures, which he himself allows to be the rule of decision and determination; and so may be said to be self-condemned. ~John Gill

So, what have we learned?  The church is no place for heresy.  Heresy is an unsound life.  Avoid heretics.  A heretic is a professed believer who maintains religious opinions contrary to those accepted by his or her church or rejects doctrines prescribed by that church [from the Word of God].

True biblical counselling, whether from the ministry or from your own personal Bible study is in close adherence to scripture and immersed in the Word of God.  It is based solely upon the Bible and focused on Christ.  All this is the lesson of verse 11.