Can you believe something God has never said?
No, you cannot believe something God has never said. A person can only believe after God has spoken it; no one took God ahead of time and presumed what He would say. The gospel concerning salvation by His shed blood, death, burial, and resurrection was kept secret since the world began, so it could not be believed until revealed.
Les teaches that everything concerning what we call the gospel was still hid in the mind of God. He says you cannot believe something that someone has never said, and you cannot believe what God hasn't said. No one took God ahead of time and said, 'Well, I know that's what He's going to say.' They believed it after He said it. God had not yet said He would save the whole human race based on His shed blood, death, burial, and resurrection, so Peter couldn't say it. Paul later writes in Romans 16:25 about the revelation of the mystery, or secret, which was kept secret since the world began. Peter didn't know it because it hadn't been revealed yet.