'For if I do this of my own will, I have a reward. But if not of my 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 without charge, so as not to use to the full my right in the gospel.'
So he is bound to preach the Gospel. If he does it of his own will, as a free man, without receiving any payment for it, he has a reward. And that reward is that he can provide the Gospel without charge, not claiming his rights to support under the Gospel. On the other hand, if he does not do it of his own will (as he has just suggested), but as a slave, it is because the stewardship of the Gospel has been entrusted to him. But either way he is rewarded in that he can make the Gospel without charge, and thus not use to the full his right in the Gospel to claim maintenance.
Thus will all see that it is his very life, that he is genuine in what he is doing. They will see that he does not preach in order to earn a living, as did so many of the preachers, teachers and philosophers who went around teaching in order to do so. Rather they may know that he does it because it is his trust, his calling, his life work, a demand that God makes on him, for which he seeks nothing but the glory of God.