A disciple must follow the teachings of Christ. A true disciple must follow completely all the teachings of Jesus Christ. Because we are the disciples of Jesus Christ, we must follow his teachings. We must obey everything that Jesus teaches us in the doctrines. We must keep to the instructions and the doctrines which he gave to the apostles. The Bible says that the disciples of old continued daily in the apostles doctrines. There were always following those doctrines. The same doctrines were handed down to us by the apostles. So we also should follow all the doctrines as true disciples of Jesus Christ.
It is not only the 12 apostles who were the only disciples. The disciples are all those who have come to accept the teachings which the apostles taught them. Everyone who has come to accept the doctrines of the church of God is a disciple of Jesus Christ. It is not enough for us to just hear the doctrines, we must obey them. We must follow all the teachings of Jesus Christ.