What is the gospel we must believe to be saved?
The gospel to believe for salvation is the gospel of the grace of God: that Christ died, shed His blood, was buried, and rose from the dead. God has revealed this as all that is necessary, and salvation is by faith plus nothing in what He has proclaimed.
Les teaches that the secret things belong to the Lord, and a person does not believe something until God says it. Adam and Abraham did not understand the Gospel because it had not yet been revealed; it was kept secret in the mind of God. But when God revealed the Gospel of the grace of God—that Christ died, shed His blood, was buried, and rose from the dead—He said that is all that is necessary for salvation. Now He expects us to believe it, because He has revealed it. Salvation is by faith plus nothing in that which God has now proclaimed. Faith comes by hearing, and hearing the Word of God.