Jamieson, Fausset & Brown

"Some indeed are preaching Christ even for envy, that is, to carry out the envy which they felt towards Paul, on account of the success of the Gospel in the capital of the world, owing to his steadfastness in his imprisonment; they wished through envy to transfer the credit of its progress from him to themselves. Probably Judaizing teachers (Rom. 14:1-23; Co1 3:10-15; Co1 9:1, &c.; Co2 11:1-4). some also of--rather, "for" good will--answering to "the brethren" (Phi 1:14); some being well disposed to him.