What important change did Paul make to Christianity?

Paul did not make any changes to Christianity. Jesus Christ is the Author of Christianity and it did not need changing, but there were times when Paul had to explain the "right" way that God wanted us to go. Christianity was just an infant in Paul's time and I am sure Paul prayed to God many times to go the right direction. At one time he and the leaders at the Jerusalem church had a council to be sure they agreed on what Christ wanted them to do.