Paul’s Own (and Only) Gospel

What does Paul mean in his letter to the Galatians when he says that he did not receive his gospel from humans but direct from God through a revelation of Jesus? Does he mean that he was the one (through direct divine inspiration) who came up with the idea that it was the death and resurrection of Jesus, rather than, say, Jesus’ life and teachings, that brings salvation? And if so, doesn’t that mean that Paul himself would be the founder and creator of Christianity, since Christianity is not...