In a world of many faiths, what is the “one faith”? Seeking the answer, we explore the ministry of Paul who wrote about “one faith” in Ephesians. Paul was God’s special missionary to welcome Gentiles into the church. He defended them against a different faith insisted on by some Jewish Christians. They believed that Gentiles had to be circumcised like Jews. Paul’s letter to the Ephesians reflected the apostles’ position as recorded in Acts 15: God saves through faith in Christ, not by works of the Law of Moses. So great is God’s grace, even for Gentiles just rescued from vile sins, that God makes them His children. “In Christ” they are full members and heirs in His one, united family. In all this, faith is central. But what is faith? Is it a feeling? Is it saying, “Lord, Lord”? Jesus and Paul define faith in terms of obedience, which is to say, “faith working through love.” In Ephesians, faith walks in a manner worthy of Christ’s high calling.