It's in THE BOOK

God never chooses one of the eleven disciples to reveal what happened at Calvary but chose a persecutor of the church, a very religious, observer of the Law, an individual named Saul. Later, after his conversion, the mystery of the gospel is revealed to him by the revelation of Jesus Christ. He (Paul) becomes the very first and only to preach, teach, and write about how that Christ died for our sins, was buried, and rose again the third day, which is to be known as the Gospel of the Grace of God.