From First Corinthians by George T. Montague, SM, commenting on I Corinthians 3:9c-11, 16-17
Paul develops the image of the Church as God’s building, but from the viewpoint of the builders, meaning the ministers, with Paul himself as the first. Speaking from his own experience, he recalls that it was according to the grace of God given to me: thus it was God’s choice, not his, that he should be a founder of churches in Gentile territory. He does not hesitate to call himself a wise master builder.
His task was to lay a foundation on which others could build. That is why Paul did not settle in one place very long. He would invest as much time as necessary to give the new community sufficient stability, appoint local leaders, and move on. This policy shows an enormous trust both in the Holy Spirit and in the fledgling leadership in whose hands he left the community.
But he warns the Corinthians against any builder who would lay a different foundation than the one Paul has already laid: Jesus Christ. This was no small matter in a place like Corinth, where every imaginable cult had its hawkers, and syncretism — the mixing of elements from various religions — was rife. Others not of apostolic origin could introduce pagan or even Jewish extraneous elements and dilute or transform the gospel into an unrecognizable counterfeit.
But even assuming that the minister builds on Paul’s foundation, the quality of his work may vary, from gold to straw. The first three elements Paul mentions are not combustible, the last three are. Paul, then, has been like the master contractor who, after laying the foundation, has let out the rest to subcontractors. If these build well, their work will stand on the day of judgment, biblically associated with fire (Dan 7:9–10; Mal 4:1–2; 2 Pet 3:7).