Up to now I am so far restored in that glory that I confess I am ignorant not only how near I come to it but even whether I shall come to it at all. It is true I am a dispenser of eternal salvation along with my other innumerable fellow servants. “For if I do this thing willingly, I have a reward.” To be a dispenser of that salvation by word and sacrament is not at all the same as to be a partaker of it. Letter , To Audax.
For if I do this thing willingly I have a reward. That Isaiah , as Chrysostom, Theophylact, Å’cumenius, and Anselm say, if I freely preach without charge, I have not merely the reward given to a work that has been enjoined on me, as other Apostles have, but the exceeding reward of abounding glory given to a work not enjoined, but heroically undertaken by a soul that is of its own accord generous towards God.
But if against my will. Compelled by a command of God, or under fear of punishment. Willingly here denotes the doing a thing of one"s own motion, one"s own accord, and free will; unwillingly, the doing it under order, being moved and forced by the will of another.
A dispensation of the gospel is committed unto me. I shall not have that supreme glory I spoke of, but neither shall I sin, because I fulfil my duty, and do what I am ordered. For this commission of preaching the Gospel was intrusted to me. But though I do not sin, yet I act as a slave, or as a steward in matters intrus...
But if against my will. That is, if I do not do it with alacrity and zeal, but instigated by the sole motive of punishment, woe unto me, as he says in the preceding verse, if I am instigated by this motive alone; still the dispensation of the gospel is entrusted to me, and I must comply with that obligation, either with the zeal and alacrity of a son, or for fear of punishment, as a slave. (Estius)