In 1 Corinthians 3, Paul draws pictures to show the nature of effective evangelism. He uses farming to illustrate that God coordinates the entire process and provides growth and fruit. The human part is merely to plant and to water (1 Corinthians 3:6-8). Then Paul changes to a picture of constructing a building.
You are God’s field, God’s building. According to the grace of God given to me, like a skilled master builder I laid a foundation, and someone else is building upon it. Let each one take care how he builds upon it. For no one can lay a foundation other than that which is laid, which is Jesus Christ. Now if anyone builds on the foundation with gold, silver, precious stones, wood, hay, straw—each one’s work will become manifest, for the Day will disclose it, because it will be revealed by fire, and the fire will test what sort of work each one has done. If the work that anyone has built on the foundation survives, he will receive a reward. If anyone’s work is burned up, he will suffer loss, though he himself will be saved, but only as through fire (1 Corinthians 3:9-15).
Jesus Himself is the one and only foundation for effective evangelism. Without Him, we can do nothing (John 15:5). Now, we turn to effective building on that foundation. We heed Paul’s warning, “Let each one take care how he builds” upon the foundation (1 Corinthians 3:10). We want to construct carefully and effectively.