Romans 16: 17-20
“Now I beseech you, brethren, mark them which cause divisions and offenses contrary to the doctrine which ye have learned and avoid them. For they that are such serve not our Lord Jesus Christ, but their own belly, and by good words and fair speeches deceive the hearts of the simple. For your obedience is come abroad unto all men. I am glad, therefore, on your behalf; but yet I would have you wise unto that which is good, and simple concerning evil. And the God of peace shall bruise Satan under your feet shortly. The grace of our Lord Jesus Christ be with you! Amen.”
The following explication of this text is from The Popular Commentary of the Bible by Dr. Paul Kretzmann:
This warning comes into the postscript in the nature of an after-thought. Very likely the congregation at Rome had not yet been troubled, but Paul feels it necessary to warn his Christians against a danger which might strike them at any time. It is not the open enemies of the Christian Church that work the greatest harm, but the false teachers that call themselves after the name of Christ and purport to believe in, and to teach, the Bible, and who, by insidious propaganda, subvert the foundations of sound teaching.
St. Paul, therefore, warns the believers at Rome and the Christians of all times against such people as teach a doctrine at variance with the plain truths as he has proclaimed them. He begs them, as Christian brethren, most earnestly to mark them, literally, to keep their eye on them, to be on the constant lookout for them, that cause factions and scandals contrary to the doctrine which they had learned, which had been preached in Rome all these years, and to turn away from these false teachers.
The apostle may have had in mind such opponents and disturbers of the peace as had attempted to hinder the course of the Gospel in Antioch, in Galatia, and in Achaia. Such men would undoubtedly try to enter into the congregation at Rome also and to spread their false teaching. But Paul distinctly tells the Roman Christians and the true believers of all times that they are not only to reject the false doctrine, but also to avoid the false teachers of every kind and degree. It is the express will of God that Christians and Christian organizations with sound Biblical basis must separate themselves, and remain separate, from all denominations in which false doctrine and false teachers are permitted. All unionism, which attempts to unite truth and falsehood in the same church organization, is clearly condemned in this passage. Cp. 2 Thess. 3, 6; Titus 3, 10; 1 Cor. 5, 11; 2 John 10.