1 Corinthians 9:17

17.For if I do this thing willingly By reward here is meant what the Latins term operae pretium , recompense for labor, (495) and what he had previously termed glorying Others, however, interpret it otherwise — as meaning that a reward is set before all who discharge their duty faithfully and heartily. But, for my part, I understand the man who does this thing willingly, to be the man who acts with such cheerfulness, that, being intent upon edifying, as his one object of desire, he declines nothing that he knows will be profitable to the Church; as, on the other hand, he terms those unwilling, who in their actings submit, indeed, to necessity, but act grudgingly, because it is not from inclination. For it always happens that the man who undertakes any business with zeal, is also prepared of his own accord to submit to everything, which, if left undone, would hinder the accomplishment of the work. Thus Paul, being one that acted willingly, did not teach in a mere perfunctory manner, but left nothing undone that he knew to be fitted to promote and further his doctrine. This then was his recompense for labor, (496) and this his ground of glorying — that he did with readiness of mind forego his right in respect of his applying himself to the discharge of his office willingly and with fervent zeal.

But if unwillingly, a dispensation is committed to me. In whatever way others explain these words, the natural meaning, in my opinion, is this — that God does not by any means approve of the service done by the man who performs it grudgingly, and, as it were, with a reluctant mind. Whenever, therefore, God has enjoined anything upon us, we are mistaken, if we think that we have discharged it aright, when we perform it grudgingly; for the Lord requires that his servants be cheerful, (2 Corinthians 9:7,) so as to delight in obeying him, and manifest their cheerfulness by the promptitude with which they act. In short, Paul means, that he would act in accordance with his calling, only in the event of his performing his duty willingly and cheerfully.