John Chrysostom, on 1Cor 9:16

"For if I preach the Gospel, I have nothing to glory of; for necessity is laid upon me; for woe is unto me, if I preach not the Gospel! For if I do this of mine own will, I have a reward: but if not of mine own will, I have a stewardship entrusted to me. What then is my reward? That when I preach the Gospel, I may make the Gospel of Christ without charge, so as not to use to the full my right in the Gospel."

What sayest thou? tell me. "If thou preach the Gospel, it is nothing for thee to glory of, but it is, if thou make the Gospel of Christ without charge?" Is this therefore greater than that? By no means; but in another point of view it hath some advantage, inasmuch as the one is a command, but the other is a good deed of my own free-will: for what things are done beyond the commandment, have a great reward in this respect: but such as are in pursuance of a commandment, not so great: and so in this respect he says, the one is more than the other; not in the very nature of the thing. For what is equal to preaching; since it maketh men vie even with the angels themselves. Nevertheless since the one is a commandment and a debt, the other a forwardness of free-will, in this respect this is more than that. Wherefore he saith, explaining the same, what I just now mentioned:

"For if I do this of mine own will, I have a reward, but if not of mine own will, a stewardship is entrusted to me;" taking the words of mine own "will" and "not of mine own will," of its being committed or not committed to him. And thus we must understand the expression, "for necessity is laid upon me;" not as though he did aught of these things against his will, God forbid, but as though he were bound by the things commanded, and for contradistinction to the liberty in receiving before mentioned. Wherefore also Christ said to the disciples, "When ye have done all, say, We are unprofitable servants; for we have done that which was our duty to do."

"What then is my reward? That when I preach the Gospel, I may make the Gospel without charge." What then, tell me, hath Peter no reward? Nay, who can ever have so great an one as he? And what shall we say of the other Apostles? How then said he, "If I do this of mine own will I have a reward, but if not of mine own will, a stewardship is entrusted to me?" Seest thou here also his wisdom? For he said not, "But if not of mine own will," I have no reward, but, "a stewardship is committed unto me:" implying that even thus he hath a reward, but such as he obtains who hath performed what was commanded, not such as belongs to him who hath of his own resources been generous and exceeded the commandment.

"What then is the reward? That, when I preach the Gospel," saith he, "I may make the Gospel without charge, so as not to use to the full my right in the Gospel." See how throughout he uses the term "right," intimating this, as I have often observed; that neither are they who receive worthy of blame. But he added, "in the Gospel," partly to show the reasonableness of it, partly also to forbid our carrying the matter out into every case. For the teacher ought to receive, but not the mere drone also.