"For I did not receive it from any man, nor was I taught it, but I received it through a revelation of Jesus Christ." - Galatians 1:12 In Paul's letter to the Galatians, he spends a bit of time explaining the way in which he was called. As many of us know, his experience came on the road to Damascus when Jesus stepped in front of him, blinded him, and saved him. The entire account is remarkable but what strikes me most is Paul's statement in verse 12 of chapter 1 where he says he was not taught the gospel but received it.
It might be fair to say then that the gospel is not something we learn like we would mathematics, with each piece building to a more complicated whole, but rather it is something we receive like a birth mark. If we've received the gospel, it never leaves us.