Paul says that the Gospel of God was given beforehand through the prophets. We look into the ministry that the prophets had. They served two purposes, first in telling people how God wanted them to live and then in pointing people to the coming Messiah.
We see that the office of prophet has ceased with the coming of Christ, since God’s revelation is complete. It is now the responsibility of elders to tell people from God’s Word how they should live and all of us need to tell others how they may be saved in Christ.
We compare the true Gospel that Paul taught with the false Gospels taught by more recent ‘prophets’ and see that they are completely different.
We are encouraged to play our role in telling others this Gospel so that they might be saved by the only way that God has appointed.