Paul believed that by Christ’s death and resurrection a person is put into a restored relationship with God. He had several ways of explaining how it worked. But in all of these ways, it was Jesus’ death and resurrection that mattered. It was not keeping the Jewish law. It was not knowing or following Jesus’ teaching. It was not Jesus’ miracles. It was not … anything else. It was Jesus’ death and resurrection.
The teaching of Jesus himself was about the coming Son of Man and the need to prepare by keeping the Law of God, as revealed in the Torah, as summarized in the commandments to love God above all else and to love one’s neighbor as oneself.
Paul didn’t invent Christianity, he inherited his understanding of the death and resurrection of Jesus from those who came before him, even if he understood its significance for Gentiles differently from his predecessors.
Is the gospel that Paul preached essentially the same or different from the message of Jesus?
They are fundamentally different.