The one preach Christ of contention - So as to form parties, and to produce strifes among his professed followers.
Not sincerely - Not “purely” - ἁγνῶς hagnōs - not with pure motives or intentions. Their real aim is not to preach Christ, but to produce difficulty, and to stir up strife. They are ambitious people, and they have no real regard for the welfare of the church and the honor of religion.
Supposing to add affliction to my bonds - To make my trial the greater. How they did this is unknown. Perhaps they were those who were strongly imbued with Jewish notions, and who felt that his course tended to diminish respect for the law of Moses, and who now took this opportunity to promote their views, knowing that this would be particularly painful to him when he was not at liberty to meet them openly, and to defend his own opinions. It is possible also that they may have urged that Paul himself had met with a signal reproof for the course which he had taken, and, as a consequence, was now thrown into chains. Bloomfield suggests that it was the opinion of many of the ancient expositors that they endeavored to do this by so preaching as to excite the fury of the multitude or the rulers against Paul, and to produce increased severity in his punishment. But the way in which they did this is unknown, and conjecture is altogether useless.