Jesus was a true Jew, who's mission was to bring the backslidden Judean Jews back into the True Judaism fold. Jesus came to seek and to save that which was lost...by preaching the good news that the kingdom is going to be resurrected. Babylon was the seat of Judaism for hundreds of years, and sent several prophets to Jerusalem to try to bring the Jerusalem Jews back into the fold. Those prophets were the ones who Jesus lamented about having been killed by Jerusalem. John T.B. and Jesus were just 2 in a line of prophets who tried to revive backslidden Judean Judaism.
Paul was the only apostle who understood the true gospel as well as Jesus did.
Why do you think Paul was a usurper?