Paul identified himself as "an Apostle of Jesus Christ" in his several letters to the various Churches he founded. He had previously been a merciless persecutor of the Christian Church; but after a dramatic conversion experience while en route to Damascus, he became Christianity's foremost spokesman. Paul never pretended to displace the message of the other Apostles; however he was much more successful than any of them in spreading the Gospel of Christ (Gospel meaning "good news") to Gentiles. Most of the early Apostles converted only Jews; Paul carried his message to the Gentiles after he was rejected by a number of early Christian (and therefore formerly Jewish) leaders. By the time Paul was preaching, most of the original Apostles were dead. The Church has not abandoned the message of the earlier Apostles any more than Jesus abandoned the message of the Old Testament. You will recall he said that he had come to fulfill the law. Paul's ministry in essence fulfilled the ministry began by Jesus and the earlier Disciples.