"Old Testament contains the Gospel.
In the verse following the one last quoted we read, "Unto whom it was revealed, that not unto themselves, but unto us they did minister the things which are now reported unto you by them that have preached the Gospel unto you with the Holy Ghost sent down from heaven." 1 Peter 1:12.
That is, the prophets, Moses among them, ministered the very same things that were preached by the apostles, namely, the Gospel.
Since the Gospel of God is "concerning His Son Jesus Christ our Lord," and the Jews would necessarily have believed in Jesus if they had believed Moses,
it follows that what Moses
wrote was the Gospel."
E.J. Waggoner