Note 1 at Ro 16:17: This is one of many times that Paul made a very clear statement about withdrawing from individuals who are causing problems in the church (1Co 5:9-11; Php 3:17; 2Th 3:6, 14-15; 1Ti 6:3-5; 2Ti 2:16-17, 3:5; 1Jo 2:19; and Tit 3:9-10). We also have an example of Paul separating the true believers from the false and meeting in a separate place in Ac 19:9. These are scriptural precedents for separation based on doctrine.

However, Paul did not say to avoid contact with people who simply had different doctrine. He said to avoid those who caused division and offenses over doctrine. Some people have doctrines that disagree with the Word, but they aren't disagreeable. These people can be loved and restored, but those who are causing dissension over doctrine are to be treated as contaminated and infectious.

One example of this that Paul used in this epistle was the matter of observing dietary laws. Paul made it clear that there was nothing wrong with any food (see note 12 at Ro 14:14), but it would be sin for people to eat certain foods if they weren't eating them in faith (Ro 14:23). Therefore, there can be differences of doctrines, but Paul told those that were strong in grace to bear with those who were not. However, if the weak brethren became contentious over their doctrine of abstinence from certain meats and began to condemn others (see note 3 at Ro 14:1), Paul would say to mark those people and avoid them.

The first thing Paul said to do was to mark these people. The Greek word that was translated "mark" here is the word "SKOPEO," and it means "to take aim at (spy), i.e. (figuratively) regard" (Strong's Concordance). In modern-day terms, we'd say we should "keep an eye" on these people. They are not to be trusted and should not be given the freedom to move about freely among the believers and spread infection.

The way we choose who is to be marked is based on the doctrine of God's Word. There are those who are indifferent to or don't believe the Word of God, but they aren't out to oppose it. Those, we simply love and continue to share the Word with, praying for their eyes to be opened. However, those who actively seek to subvert others from following the doctrine of God's Word are the ones to mark. Paul gave some characteristics of these people in Ro 16:18.

Marking these individuals falls into the category of church discipline and should be done consistently with all those instructions (see note 5 at Mt 18:17).