I would like to further call your attention to this one passage and various commentary that may be helpful to you:

2Th 3:14 And if any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed.

It appears in my research that I cannot find even one Biblical scholar who would agree with your assessment of this passage that Paul is, 1) limiting sins that should cause us to disfellowship brethren, or 2) limiting "if any man obey not our word by this epistle", to apply to only a portion of this epistle.

For your study and continued thought:

Burton Coffman: This is a further word on what was meant above by "withdraw yourselves." It is all social intercourse, visitation, companioning with offenders that must be ceased. Christians are simply not to mix with persons living in open rebellion against the teachings of the Lord. The purpose of such an ostracism is that it might produce shame and repentance on the part of the offender and result in his restoration.

James Meadows: A man’s obedience to the things Paul writes is made the test of whether he is to continue in the fellowship of the faithful.

The inspired Scriptures are the standard of our acceptance with God; only those who are obedient to the Scriptures have the right to fellowship with the redeemed. If a Christian ceases to faithfully obey the word of God, the other saints are to withdraw their fellowship with him. They are not to have company with him.

Adam Clarke: If any man obey not—They had disobeyed his word in the first epistle, and the Church still continued to bear with them; now he tells the Church, if they still continue to disregard what is said to them, and particularly his word by this second epistle, they are to mark them as being totally incorrigible, and have no fellowship with them.

Gospel Advocate: 14 And if any man obeyeth not our word by this epistle, — Paul makes obedience to the things he teaches in this Epistle a test of discipleship. He did the same in the first Epistle. (4:3-7.) He did this because he wrote under the inspiration of the Holy Spirit, and to obey that which was thus taught is to obey God.

note that man, —The first step was to discriminate between those who obeyed and those who did not. The second was to note him as disobedient.

that ye have no company with him, —Refuse him that social companionship that would encourage him in the wrong way. While refusing to regard him as walking as an orderly Christian should, they were yet to admonish him as a brother to return to an orderly walk in the Lord.

to the end that he may be ashamed. —While they were required to keep no company with them, they were not to count him as an enemy, but to entreat and admonish him as a brother. The apostle says: "I wrote unto you not to keep company, if any man that is named a brother be a fornicator, or covetous, or an idolater, or a reviler, or a drunkard, or an extortioner; with such a one no, not to eat." (1 Cor. 5:11.) Discipline consists in admonishing, warning, and persuading; in separating them for a time from the fellowship of the church, yet continuing to admonish as a brother before the final exclusion comes. Cutting one off is not discipline; it is the end and failure of discipline. The steps taken to save one is the discipline.

Gill: "in matters of heaven (of God or religion), if a man does not return privately, מכלימין, they "put him to shame" publicly; and publish his sin, and reproach him to his face, and despise and set him at nought until he returns to do well.''


Matthew Henry: 2Th 3:6-15 -
The apostle having commended their obedience for the time past, and mentioned his confidence in their obedience for the time to come, proceeds to give them commands and directions to some who were faulty, correcting some things that were amiss among them. Observe, The best society of Christians may have some faulty persons among them, and some things that ought to be reformed. Perfection is not to be found on this side heaven: but evil manners beget good laws; the disorders that Paul heard of as existing among the Thessalonians occasioned the good laws we find in these verses, which are of constant use to us, and all others whom they may concern. Observe,
I. That which was amiss among the Thessalonians, which is expressed,
1. More generally. There were some who walked disorderly, not after the tradition they received from the apostle, 2Th_3:6. Some of the brethren were guilty of this disorderly walking; they did not live regularly, nor govern themselves according to the rules of Christianity, nor agreeably to their profession of religion; not according to the precepts delivered by the apostle, which they had received, and pretended to pay a regard to. Note, It is required of those who have received the gospel, and who profess a subjection to it, that they live according to the gospel. If they do not, they are to be counted disorderly persons.
2. In particular, there were among them some idle persons and busy-bodies, 2Th_3:11. This the apostle was so credibly informed of that he had sufficient reason to give commands and directions with relation to such persons, how they ought to behave, and how the church should act towards them. (1.) There were some among them who were idle, not working at all, or doing nothing. It does not appear that they were gluttons or drunkards, but idle, and therefore disorderly people. It is not enough for any to say they do no hurt; for it is required of all persons that they do good in the places and relations in which Providence has placed them. It is probable that these persons had a notion (by misunderstanding some passages in the former epistle) concerning the near approach of the coming of Christ, which served them for a pretence to leave off the work of their callings, and live in idleness. Note, It is a great error, or abuse of religion, to make it a cloak for idleness or any other sin. If we were sure that the day of judgment were ever so near, we must, notwithstanding, do the work of the day in its day, that when our Lord comes he may find us doing. The servant who waits for the coming of his Lord aright must be working as his Lord has commanded, that all may be ready when he comes. Or, it may be, these disorderly persons pretended that the liberty wherewith Christ had made them free discharged them from the services and business of their particular callings and employments in the world: whereas they were to abide in the same calling wherein they were called of God, and therein abide with God, 1Co_7:20, 1Co_7:24. Industry in our particular callings as men is a duty required of us by our general calling as Christians. Or perhaps the general charity there was then among Christians to their poor brethren encouraged some to live in idleness, as knowing the church would maintain them: whatever was the cause, they were much to blame. (2.) There were busy-bodies among them: and it should seem, by the connection, that the same persons who were idle were busy-bodies also. This may seem to be a contradiction; but so it is, that most commonly those persons who have no business of their own to do, or who neglect it, busy themselves in other men's matters. If we are idle, the devil and a corrupt heart will soon find us something to do. The mind of man is a busy thing; if it be not employed in doing good, it will be doing evil. Note, Busy-bodies are disorderly walkers, such as are guilty of vain curiosity, and impertinent meddling with things that do not concern them, and troubling themselves and others with other men's matters. The apostle warns Timothy (1Ti_5:13) to beware of such as learn to be idle, wandering about from house to house, and are not only idle, but tatlers also, and busy-bodies, speaking things which they ought not.
II. The good laws which were occasioned by these evil manners, concerning which we may take notice,
1. Whose laws they are: they are commands of the apostles of our Lord, given in the name of their Lord and ours, that is, the commands of our Lord himself. We command you, brethren, in the name of the Lord Jesus Christ, 2Th_3:6. Again, We command and exhort you by our Lord Jesus Christ, 2Th_3:12. The apostle uses words of authority and entreaty: and, where disorders are to be rectified or prevented, there is need of both. The authority of Christ should awe our minds to obedience, and his grace and goodness should allure us.
2. What the good laws and rules are. The apostle gives directions to the whole church, commands to those disorderly persons, and an exhortation to those in particular who did well among them.
(1.) His commands and directions to the whole church regard, [1.] Their behaviour towards the disorderly persons who were among them, which is thus expressed (2Th_3:6), to withdraw themselves from such, and afterwards to mark that man, and have no company with him, that he may be ashamed; yet not to count him as an enemy, but to admonish him as a brother. The directions of the apostle are carefully to be observed in our conduct towards disorderly persons. We must be very cautious in church-censures and church-discipline. We must, First, Note that man who is suspected or charged with not obeying the word of God, or walking contrary thereto, that is, we must have sufficient proof of his fault before we proceed further. We must, Secondly, Admonish him in a friendly manner; we must put him in mind of his sin, and of his duty; and this should be done privately (Mat_18:15); then, if he will not hear, we must, Thirdly, Withdraw from him, and not keep company with him, that is, we must avoid familiar converse and society with such, for two reasons, namely, that we may not learn his evil ways; for he who follows vain and idle persons, and keeps company with such, is in danger of becoming like them. Another reason is for the shaming, and so the reforming, of those that offend, that when idle and disorderly persons see how their loose practices are disliked by all wise and good people they may be ashamed of them, and walk more orderly. Love therefore to the persons of our offending brethren, even when we hate their vices, should be the motive of our withdrawing from them; and even those who are under the censures of the church must not be accounted as enemies (2Th_3:15); for, if they be reclaimed and reformed by these censures, they will recover their credit and comfort, and right to church-privileges as brethren. [2.] Their general conduct and behaviour ought to be according to the good example the apostle and those who were with him had given them: Yourselves know how you ought to follow us, 2Th_3:7. Those who planted religion among them had set a good example before them; and the ministers of the gospel should be ensamples to the flock. It is the duty of Christians not only to walk according to the traditions of the apostles, and the doctrines they preached, but also according to the good example they set before them, to be followers of them so far as they were followers of Christ. The particular good example the apostle mentions was their diligence, which was so different from what was found in the disorderly walkers he takes notice of: “We behaved not ourselves disorderly among you (2Th_3:7), we did not spend our time idly, in idle visits, idle talk, idle sports.” They took pains in their ministry, in preaching the gospel, and in getting their own living. Neither did we eat any man's bread for nought, 2Th_3:8. Though he might justly have demanded a maintenance, because those who preach the gospel may of right expect to live by the gospel. This is a just debt that people owe to their ministers, and the apostle had power or authority to have demanded this (2Th_3:9); but he waived his right from affection to them, and for the sake of the gospel, and that he might be an example for them to follow (2Th_3:9), that they might learn how to fill up time, and always be employed in something that would turn to good account.
(2.) He commands and directs those that live idle lives to reform, and set themselves to their business. He had given commandments to this purport, as well as a good example of this, when he was among them: Even when we were with you, this we commanded you, that if any man would not work neither should he eat, 2Th_3:10. It was a proverbial speech among the Jews, He who does not labour does not deserve to eat. The labourer is worthy of his meat; but what is the loiterer worthy of? It is the will of God that every man should have a calling, and mind his calling, and make a business of it, and that none should live like useless drones in the world. Such persons do what in them lies to defeat the sentence, In the sweat of thy face shalt thou eat thy bread. It was not the mere humour of the apostle, who was an active stirring man himself and therefore would have every body else to be so too, but it was the command of our Lord Jesus Christ, that with quietness we work, and eat our own bread, 2Th_3:12. Men ought some way or other to earn their own living, otherwise they do not eat their own bread. Observe, There must be work or labour, in opposition to idleness; and there must be quietness, in opposition to being busy-bodies in other men's matters. We must study to be quiet, and do our own business. This is an excellent but rare composition, to be of an active yet quiet spirit, active in our own business and yet quiet as to other people's.
(3.) He exhorts those that did well not to be weary in well-doing (2Th_3:13); as if he had said, “Go on and prosper. The Lord is with you while you are with him. See that whatever you do, that is good, you persevere therein. Hold on your way, and hold out to the end. You must never give over, nor tire in your work. It will be time enough to rest when you come to heaven, that everlasting rest which remains for the people of God.”


Tom Wacaster: These guidelines apply to disciplinary action under certain situations. First, we learn who is to be disciplined. It is the one who "obeyeth not our word by this epistle .... "If a man -- any man -- does not submit to the directions given in this epistle (and by implication any other epistle given by inspiration), then certain attitudes should be expressed and actions should be implemented.

Second, we learn what is to be done. We are to "note" such a one. The word here is middle voice. Vine pointed out that "in the middle voice, (this means) to note for oneself, and is so used in 2 Thess. 3:14, (and) is an injunction to take cautionary note of one who refuses obedience to the Apostle's word by the Epistle." A different word is used in Rom. 16:17. There a warning is given against those who cause divisions, and again in Phil. 3:17, the word is used to observe those who walk after the example of the apostle and his fellow workers.

Although the word may be different, similar action is to be taken, as indicated by the rest of this verse in 2 Thessalonians. Upon noting that brother, we are to "have no company with him .... "Similar action was commanded for the fornicating brother in Corinth (1 Cor. 5:9-11). Vine suggested that the word in our text means "not to mingle with him, not to mix it up together," the idea being that association with such a one as that under consideration is forbidden.




Jamieson-Fausset-Brown: Verse 14. note that man -- mark him in your own mind as one to be avoided (2Th 3:6).

Note the comments, "mark him" and "one to be avoided"... which would be another way of explaining how we are to disfellowship from a non-repenting brother. We should "avoid" them. This passage harmonizes with what Paul wrote to the Romans, which you failed to address:

Rom 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.

Paul is in harmony and remains consistent in all his epistles. To "avoid" is the same as "have no company with him". Consider the Greek for these definitions if it may help you better understand.


I also encourage you to consider in harmony with what Paul writes, the following passages:

1Jo 1:7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.

Would this not imply that we should not have fellowship with a Christian brother or sister who is not walking in the light? What sins would be included in walking in darkness?

2Jo 1:9 Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son.
2Jo 1:10 If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:
2Jo 1:11 For he that biddeth him God speed is partaker of his evil deeds.

It is clear that only those who are obedient to God’s Word should have fellowship with other believers. It is clear that we should not have continued fellowship with an unrepenting brother or sister.

__________________
In Christ,
brother Sonnie

Jeremiah 6:16 Thus says the LORD: "Stand in the ways and see, And ask for the old paths, where the good way is, And walk in it; Then you will find rest for your souls. But they said, 'We will not walk in it.'