In 1 Corinthians 3, Paul refers to himself as a wise master builder.
Without a doubt, Paul says this in reference to his apostolic ministry to the Corinthians. Yet he doesn’t exalt himself. On the contrary Paul gives a very sober warning, declaring, “if any man defile the temple of God, him shall God destroy.”
Jesus Christ is the only foundation of the temple of God, and every man is going to be rewarded in the day of judgment for how he has built on the foundation of Christ.
Paul’s says the following in verses 16-20:
Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you? If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are. Let no man deceive himself. If any man among you seemeth to be wise in this world, let him become a fool, that he may be wise. For the wisdom of this world is foolishness with God. For it is written, He taketh the wise in their own craftiness. And again, The Lord knoweth the thoughts of the wise, that they are vain. ~ 1 Corinthians 3: 16-20
Paul’s words regarding the Temple of God (above) are within the context of how ministers are to build on the foundation which has been laid: Christ Jesus. Paul says this within the larger context of contrasting the wisdom of God with the wisdom of this world.
Those who do not build wisely on the foundation of Christ, but defile temple of God with the wisdom of this world (with such things as greed and carnality) are warned. They stand in jeopardy of being destroyed by God for defiling his temple, or at the very least suffering loss of reward because they built not with eternal things (see 1 Corinthians 3:13-15)
Thus the reason for Paul’s exhortation: “let every man take heed how he builds thereupon.”