Where are the mysteries of God revealed if they aren't in the Gospels or the Old Testament?

The mysteries of God are revealed throughout Paul's epistles, or letters. They are not in the Gospels, Old Testament, or even for the most part in Acts. Paul writes in 1 Corinthians 4:1 that he and others are stewards of these mysteries.

Les explains that these revelations are never referred to anywhere else in Scripture—they are not in the Gospels, not in the Old Testament, and not even in the book of Acts for the most part. Instead, they come throughout Paul's epistles, or letters. In 1 Corinthians 4:1, Paul calls himself and others ministers of Christ and stewards of the mysteries of God. Verse 2 then says it is required of stewards to be faithful in whatever they are in charge of, whether a business or a church activity.

1 Corinthians 4:1

Let a man so account of us, as of the ministers of Christ, and stewards of the mysteries of God.

Where are the mysteries that Paul talks about revealed in the Bible?

The mysteries Paul talks about are revealed throughout Paul's epistles, or letters. They are not found in the Gospels, the Old Testament, or even for the most part in the book of Acts. These appalling revelations come through Paul's writings as the revelation of the mysteries.