If any man's work remains, he will receive a reward. His meaning is, that those are fools who depend on man's estimation, so as to reckon it enough to be approved by men, for then only will the work have praise and recompense -- when it has stood the test of the day of the Lord Hence he exhorts His true ministers to have an eye to that day. For by the word remains, he intimates that doctrines fly about as it were in an unsettled state, nay more, like empty bubbles, they glitter for the moment, until they have come to be thoroughly tested. Hence it follows, that we must reckon as nothing all the applauses of the world, the emptiness of which will in a very little be exposed by heaven's judgment.

If any man's work abide - If it shall appear that he hast taught the true doctrines of Christianity, and inculcated right practices and views of piety, and himself cherished right feelings: if the trial of the great Day, when the real qualities of all objects shall be known, shall show this.
He shall receive a reward - According to the nature of his work. See the note on 1-Corinthians 3:8. This refers, I suppose, to the proper rewards on the Day of Judgment, and not to the honors and the recompense which he may receive in this world. If all that he has taught and done shall be proved to have been genuine and pure, then his reward shall be in proportion.

If any man's work abide - Perhaps there is here an allusion to the purifying of different sorts of vessels under the law. All that could stand the fire were to be purified by the fire; and those which could not resist the action of the fire were to be purified by water, Numbers 31:23. The gold, silver, and precious stones, could stand the fire; but the wood, hay, and stubble, must be necessarily consumed. So, in that great and terrible day of the Lord, all false doctrine, as well as the system that was to pass away, should be made sufficiently manifest; and God would then show that the Gospel, and that alone, was that system of doctrine which he should bless and protect, and none other.
He shall receive a reward - He has not only preached the truth, but he has labored in the word and doctrine. And the reward is to be according to the labor. See on 1-Corinthians 3:8 (note).

If any man's work abide,.... That is, if any minister's doctrine will bear the test of daylight, to be looked into, and abide the fire of the word; as gold, silver, and precious stones will, or such doctrines as are comparable to them, which will shine the brighter for being tried by this fire:
which he hath built thereupon; upon the foundation Christ, in entire consistence with, and proportion to it, and highly becoming it:
he shall receive a reward; either from the churches of Christ here, who shall honour and respect him for his faithful labours in the ministry; or from Christ hereafter, who will say, well done, good and faithful servant, enter thou into the joy of thy Lord.

abide--abide the testing fire (Matthew 3:11-12).
which he hath built thereupon--which he built on the foundation.
reward--wages, as a builder, that is, teacher. His converts built on Christ the foundation, through his faithful teaching, shall be his "crown of rejoicing" (2-Corinthians 1:14; Philippians 2:16; 1-Thessalonians 2:19).

He shall receive a reward - A peculiar degree of glory. Some degree even the other will receive, seeing he held the foundation; though through ignorance he built thereon what would not abide the fire.