What is the foundation Paul laid that our faith must rest on?

The foundation Paul laid is Jesus Christ crucified, buried, and risen from the dead. This finished work is the secure ground on which faith must rest, not the wisdom of this world. Salvation is Jesus Christ plus nothing, for there is no other name given among men whereby we must be saved.

Les explains that Paul, as a wise master builder, laid the foundation, and that wisdom is tied to God's wisdom versus the wisdom of this world. Les uses the analogy of a building: the foundation is the heart of the structure, and a rotten foundation produces a rotten building, while a solid, secure foundation supports the rest. He applies this to faith: unless our faith rests on the foundation Paul laid—Christ crucified, buried, and risen from the dead—we are hopelessly lost. The world calls this exclusivism, but the teaching insists there is no other name given among men whereby we must be saved. It is Jesus Christ plus nothing, and faith in that finished work.

1 Corinthians 3:10

According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon.

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What foundation did Paul say he laid for the Gentile church?

The apostle of the Gentiles laid Jesus Christ as the foundation for the Gentile church. To this Gentile church he writes, “I have laid the foundation,” and identifies that foundation as Jesus Christ—yes, Jesus of Nazareth. It was for Jew and Gentile alike, but primarily for the Gentile because the Jew rejected it.