What is the content of the gospel that saves?

The gospel that saves is that Christ died for our sins according to the Scriptures, was buried, and rose again the third day according to the Scriptures. It is not based on Judaistic law, but on the Messiah of Israel, the Son of God, dying on the Roman cross, shedding His blood, and rising again.

Les explains that the gospel by which we are saved is what Paul delivered, having received it by revelation from the Lord. It is not based on Judaistic law, nor merely on Christ being the Messiah of Israel. Instead, it is that the Messiah of Israel, the Son of God, died on the Roman cross, shed His blood, was buried, and rose again the third day according to the Scriptures. Les emphasizes this was not an accidental martyr's death but was in the pre-eternal mind of God, and Christ was really dead and truly rose, seen by Peter, over 500, and Paul himself.

1 Corinthians 15:3

For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;

Is salvation by the Law, works, or repentance and baptism, or by believing the Gospel?

Scripture teaches that salvation is not found in the Law, not in works, and not in repentance and baptism. It is found in believing the Gospel: that Christ died for our sins, was buried, and rose again the third day according to the Scriptures.