Romans 16:18

Their own belly. — Compare the description in Philippians 3:18, where the Apostle is also denouncing certain persons who made “a god of their belly.” It is not, however, quite clear that the class of persons intended is precisely the same. There the Apostle is condemning Antinomian extravagances which professed to be based on his own teaching; here he would seem to have in view some more radical divergence of doctrine, “contrary to” that which they had learned. Selfish indulgence is unfortunately a common goal, to which many diverse ways of error will be found to lead.

By good words and fair speeches. — The difference, perhaps, is between “insinuating” or “specious” address, and “fine phrases” in a rhetorical sense.

Simple. — Literally, guileless. Those who have no evil intentions themselves, and do not readily suspect others of them.