Adam Clarke on Romans 16:17

Mark them which cause divisions - Several MSS. read ασφαλως σκοπειτε, look sharply after them; let them have no kiss of charity nor peace, because they strive to make divisions, and thus set the flock of Christ at variance among themselves; and from these divisions, offenses (σκανδαλα, scandals) are produced; and this is contrary to that doctrine of peace, unity, and brotherly love which you have learned. Look sharply after such that they do you no evil, and avoid them - give them no countenance, and have no religious fellowship with them.