For if I do this thing willingly By reward here is meant what the Latins term operae pretium, recompense for labor, [1] 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, [2] 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.

Footnotes

1 - "Ce que nous appelons chef-d'oeuvre;" -- "What we call a masterpiece." The idiomatic phrase, operae pretium, is ordinarily employed by the classical writers to mean -- something of importance, or worthwhile. Thus Livy, in his Preface, says: "facturusne operae pretium sim;" -- "whether I am about to do a work of importance," and Cicero (Cat. 4. 8) says: "Operae pretium est;" -- "It is worth while." Calvin, however, seems to make use of the phrase here in a sense more nearly akin to its original and literal signification -- recompense for labor -- what amply rewarded the self-denial that he had exercised -- consisting in the peculiar satisfaction afforded to his mind in reflecting on the part that he had acted. The term made use of by him in his French Translation -- chef-d'oeuure (masterpiece) corresponds with the Latin phrase operae pretium in this respect, that a masterpiece is a work, which the successful artist, or workman, sets a value upon, and in which he feels satisfaction, as amply recompensing the pains bestowed. -- Ed.

2 - "Son chef-d'oeuure;" -- "His masterpiece."

For if I do this thing willingly - If I preach so as to show that my heart is in it; that I am not compelled, If I pursue such a course as to show that I prefer it to all other employments. If Paul took a compensation for his services, he could not well do this; if he did not, he showed that his heart was in it, and that he preferred the work to all others. Even though he had been in a manner compelled to engage in that work, yet he so acted in the work as to show that it had his hearty preference. This was done by his submitting to voluntary self-denials and sacrifices in order to spread the Saviour's name.
I have a reward - I shall meet with the approbation of my Lord, and shall obtain the reward in the world to come, which is promised to those who engage heartily, and laboriously, and successfully in turning sinners to God; Proverbs 11:30; Daniel 12:3; Matthew 13:43; Matthew 25:21-23; James 5:20.
But if against my will - (ἄκων akōn). "If under a necessity 1-Corinthians 9:16; if by the command of another" (Grotius); if I do it by the fear of punishment, or by any strong necessity which is laid on me.
A dispensation of the gospel is committed unto me - I am entrusted with (πεπίστευμαι pepisteumai) this dispensation, office, economy (οἰκονομίαν oikonomian) of the gospel. It has been laid upon me; I have been called to it; I must engage in this work; and if I do it from mere compulsion or in such a way that my will shall not acquiesce in it, and concur with it, I shall have no distinguished reward. The work must be done; I must preach the gospel; and it becomes me so to do it as to show that my heart and will entirely concur; that it is not a matter of compulsion, but of choice. This he proposed to do by so denying himself, and so foregoing comforts which he might lawfully enjoy, and so subjecting himself to perils and toils in preaching the gospel, as to show that his heart was in the work, and that he truly loved it.

For if I do this thing willingly - If I be a cordial co-operator with God, I have a reward, an incorruptible crown, 1-Corinthians 9:25. Or, if I freely preach this Gospel without being burthensome to any, I have a special reward; but if I do not, I have simply an office to fulfill, into which God has put me, and may fulfill it conscientiously, and claim my privileges at the same time; but then I lose that special reward which I have in view by preaching the Gospel without charge to any.
This and the 18th verse have been variously translated: Sir Norton Knatchbull and, after him, Mr. Wakefield translate the two passages thus: For if I do this willingly, I have a reward; but if I am intrusted with an office without my consent? what is my reward then? to make the Gospel of Christ, whilst I preach it, without charge, in not using to the utmost my privileges in the Gospel.
Others render the passage thus: But if I do it merely because I am obliged to it, I only discharge an office that is committed to me, 1-Corinthians 9:18. For what then shall I be rewarded? It is for this, that, preaching the Gospel of Christ, I preach it freely, and do not insist on a claim which the Gospel itself gives me.

For if I do this thing willingly,.... That is, not freely and without receiving anything for preaching, without seeking any temporal profits and advantages; nor in pure love to Christ, and the good of souls, without any fear of punishment, or hope of reward; but the apostle supposes a case which was not, and his sense is, that supposing no necessity had been laid upon him, or any injunction or command given him to preach the Gospel, but he had entered on it without any obligation upon him, then, says he,
I have a reward; or should have one, or might expect one; so the Jews (q) say, that a reward is given to him, who does anything unbidden:
but if against my will, or unwillingly,
a dispensation of the Gospel is committed to me; which was his case; the Gospel was committed to his trust, as anything is to the trust and charge of a steward by his lord, who is obliged to take care of it, and is accountable for it, and of whom faithfulness is required; he did not undertake this economy, or dispensation of the Gospel of himself, of his own mind and will, but it was enjoined him by one that had the command over him, and could and did oblige him to take the charge of it; though he made him willing, as well as able to do it: and therefore since this was the case, that it was not at his own option whether he would preach the Gospel or not, but he was obliged to it by one, that had a superior power and influence over him; hence, though he performed it ever so well, and with never so much faithfulness and integrity, he asks in the following verse,
(q) Maimon. apud Hammond in loc.

Translate, "If I be doing this (that is, preaching) of my own accord (which I am not, for the 'necessity' is laid on me which binds a servant to obey his master), I have a reward; but if (as is the case) involuntarily (Acts 9:15; Acts 22:15; Acts 26:16); not of my own natural will, but by the constraining grace of God; (Romans 9:16; 1-Timothy 1:13-16), I have had a dispensation (of the Gospel) entrusted to me" (and so can claim no "reward," seeing that I only "have done that which was my duty to do," Luke 17:10, but incur the "woe," 1-Corinthians 9:16, if I fail in it).

Willingly - He seems to mean, without receiving anything. St. Paul here speaks in a manner peculiar to himself. Another might have preached willingly, and yet have received a maintenance from the Corinthians. But if he had received anything from them, he would have termed it preaching unwillingly. And so, in the next verse, another might have used that power without abusing it. But his own using it at all, he would have termed abusing it. A dispensation is intrusted to me - Therefore I dare not refrain.