Faith comes by hearing, not in some general sense, but by hearing Jesus Christ speak. Jesus himself is the Son who was sent by the Father, and he “speaks the words of God, for God gives the Spirit without limit” (John 3:34, NIV). He testifies to what he has seen and heard in heaven (John 3:31-32). The words that he speaks are Spirit and life (John 6:63, 68). Paul does not suppose that every believer has heard Jesus speak in the same way that he did on the Damascus road. Paul’s hearing was part of his seeing the risen Lord. The Lord sent him as a chosen vessel to bear his name before Gentiles, kings, and the children of Israel. Paul as an apostle could speak of his gospel as that climactic revelation of the mysteries of God that enabled him to declare the word of Christ to the Gentiles as well as to the people of Israel (Eph. 3:2-12).
As God’s ambassador, Paul spoke for God, for God was speaking through him (2 Cor. 5:20). The gospel that Paul preached was not of men, received from or taught by men, but received by revelation from Jesus Christ (Gal. 1:11-12). We hear our Lord, not just in the red letters of a Bible, but in the whole revelation of the Lord, the Word.
Adapted from Preaching Christ in All of Scripture by Edmund Clowney