The following is from Dub McClish commenting on Romans 16:17, in THE BOOK OF ROMANS, edited by Elkins and Warren, 1983 Spiritual Sword Lectures, pp. 241-245

Stronger and plainer words on the necessity of maintaining doctrinal purity cannot be found in or out of the New Testament than these in Paul's final plea of the epistle.  Paul says, "I beseech you," which translates PARAKOLO.  The term is a compound of PARA, along side of or beside, and KALEO, to call, thus, to call one alongside of oneself.  It is a strong term of appealing, urging, exhorting and encouraging to a given action.  Although Paul, as an apostle, could have commanded what he writes here, he issues a strong, imploring appeal instead.   However, the exhortation nonetheless has the strength of a charge, order, or command.  This is not merely a polite suggestion, but an earnest entreaty!  The substance of the appeal is that the true doctrine of Christ which they had learned must be carefully guarded and preserved.  The principal means by which this was done were two: (1) "mark them that are causing the divisions and occasions of stumbling contrary to the doctrine," and (2) "turn away from them."  There was never a more devilish doctrine than that which teaches the unimportance of doctrinal purity and truth.  None can read the New Testament with an unprejudiced eye and keep from seeing the constant emphasis upon it. It begins with such representative statements of our Lord as, "If ye abide in my word, then are ye truly my disciples" (John 8:31) and "He that rejecteth me, and receiveth not my sayings, hath one that judgeth him:  the word that I spake, the same shall judge him in the last day" (John 12:48).  It does not end until almost the final words of the final book which sternly warn men neither to add to nor subtract from the revealed word (Rev 22:18-19).  No New Testament author neglects this emphasis.

The motive of this strong and consistent theme rests in the truth that the Word of God through Christ is God's spiritual seed.  If the seed be faithfully preserved and planted, it can do nought but produce the plant that is imprinted by God on its spiritual genes. Moreover, when the seed germinates and produces God's plant, that spiritual plant--the church--can remain pure, healthy, and strong only so long as it feeds upon the pure doctrine of the gospel.  Apostasy cannot be defined apart from doctrinal corruption.  When one or a hundred saints move away from Christ, it is because they have embraced a different"gospel"--a perverted one (Gal 1:6-7).    The reason why the church of the present is different from that of even one generation ago is because the message, the doctrine has been changed.  The two--the doctrine and the church--are inseparably linked.  When the doctrine is changed, a vicious cycle, almost incapable of being interrupted, is set in motion. The change of doctrine creates change in the church, and the more the church changes, the more the doctrine is despised, causing yet further digressions by the church.

This is why the inspired men were so boldly militant in their preservation of divine truth. As they did, so must we contend earnestly for the faith, being always ready to give answer for our hope and being set for the defense of the gospel (Jude 3; 1Pet 3:15; Phil 1:16).  This is precisely why Paul wrote this magnificent appeal to conclude his letter to Rome.  No better illustration of what happens when men ignore this appeal can be found than the totally apostate church of Rome which began as the church of Christ in Rome to whom Paul wrote this letter. 

False doctrine does not exist independent of false teachers.   Therefore, the originators and/or propagators of the divisive doctrines must be dealt with.   They are to be "marked."  "Mark"is from SKOPEIN, a present infinitive form of SKOPEO, meaning to "look (out) for, notice, keep one's eyes on someone or something." {Walter Bauer, William F. Arndt, F. Wilbur Gingrich, A GREEK-ENGLISH LEXICON OF THE NEW TESTAMENT AND OTHER EARLY CHRISTIAN LITERATURE (Grand Rapids, MI: 1957), p. 764]. There is to be a vigilance in every Christian for the false teacher.  How strange that anyone claiming loyalty to Christ and respect for New Testament teaching and example would sympathize with purveyors of perverted teaching. The only way some brethren"look out for" the teacher of contrary doctrines is to supply his needs and protect him!  Paul is demanding of us the practice of discrimination in teachers and teaching.  Quite pitifully some (including elders) are so ignorant of truth they don't recognize error when they hear or see it.  Others count it a mark of spiritual superiority never to "keep books" or "files" on any brother.  Like the fool who places his hand over the gas gauge in his car, thinking the gas will last indefinitely if he doesn't see it register "empty," so is the brother who prides himself in not knowing or taking note of who is teaching or practicing this or that, thinking it will go away if it is ignored.   A generation of ignoring instead of taking note has shown the predictable evil fruits of disobeying divine instruction. 

It has been argued that the idea of "branding" is not in the word translated "mark." [Jack P. Lewis, MARK THEM WHICH CAUSE DIVISIONS, in FIRM FOUNDATION, Feb. 22, 1983, p. 6].  This is doubtless true concerning this single word of the text.  However, does not the act of taking note of false teachers so as to be able to avoid them and to warn others of them demand that they be branded or exposed for what they are?  Was not this our Lord's practice (Matt 16:6)?  This was both the practice and precept of Paul (1 Tim 1:3, 20; 2 Tim 2:16-17; 4:1-4; Titus 1:9-13, etc.).   If Paul did not give this charge to the end that divisive teachers might be identified and exposed, then the charge has no meaning.

Not only are these teachers to be taken note of, they are to be turned away from, avoided (cf., Titus 3:10; 2 John 10-11). That is, they are not to be listened to or extended any sort of treatment that implies endorsement.  How true it is of preachers and colleges that they are known by the company they keep.  If many of our brethren had not been too "smart," sophisticated and "bleeding-heart" tolerant over the past twenty years to obey Paul's inspired instruction in this matter, we could have isolated most of the element that is leading many brethren ever closer to denominationalism.  For lack of backbone to turn away from these men, many of them are now firmly entrenched and are enjoying an increasing popularity.

This passage emphasizes the dependence of true unity upon doctrine.  The concept of the possibility of scriptural unity on any basis that ignores or forfeits doctrinal truth must be rejected.  There can be no heaven-ordained unity in the climate of doctrinal diversity.  Scriptural unity surely involves mutual love between the parties concerned, but it requires far more than mere love.  This passage states it plainly: where doctrines that differ from and are contrary to THE DOCTRINE are taught and received, the result is not unity, but "divisions and occasions of stumbling." Such statements as "It is not doctrine that unites us, it is love," are not only unscriptural, they are totally anti-scriptural.  The content of Romans 16:17 alone is sufficient successfully to challenge the insidious Ketcherside-Garrett doctrine of "unity in diversity."  

In the face of divisive, destructive doctrines that are contrary to "the doctrine" many yet cry for patience and tolerance toward teachers of the same.   Just how long can false teachers be allowed to ravish the bride of Christ?   For example, how long must we wait to apply this order to men on who are propagating divisive and contrary doctrines on marriage, divorce, and remarriage?   These doctrines are leading many to live in fornication with no sense of guilt.   Already many congregations under the influence of such teachers have become open havens for the unscripturally divorced and remarried.  If we think the influence of these doctrines on the present generation is a tragedy, just wait until a second generation grows up under them! 

Are these doctrines causing division?  Most certainly!   It is happening both at home and abroad.  I have some heart-breaking letters in my files, received in the past year of grievous divisions in Thailand, or problems in Ghana, of grave fears of good brethren concerning Korea, Taiwan, and the Philippines relating to these doctrines.  If now is not the time for faithful brethren to stand up and say, "We have taken note of these false teachers and their divisive doctrines and we must turn away from them," then when will be the time?  How many more young preachers and uninformed elders will they be allowed to influence?  How many more churches must be divided, and how many more souls lost before we draw the line and say, "This far and no further?" 

As sad as it is to consider and as difficult as it is to do, can we any longer resist the Holy Spirit's instruction? It is not my place to command others nor to decide for others on this matter.  However, for my part I have taken note of these men and their doctrines some time ago, and I have turned away from them.   I will not knowingly use them, work with them, nor encourage them.  If our brotherhood would as one man obey Paul's order concerning the teachers of these doctrines, some of them would surely be brought to repentance.  If not, at least their influence would be all but neutralized, if not nullified.  As it is, they are "not serving our Lord Christ" and many are being "beguiled by their smooth and fair speech.