The gospel is one. We don't have different doctrines.
From Genesis to Revelation talk about one person and that is Jesus Christ. There is no other messages. We have one message. John 5:39.
The message is all about the birth, the death, the resurrection and the glorification of Jesus ( Ascension)
Christianity is Apostolic. Meaning what Jesus preached the apostles preached and what the apostles preached we also preach. The same message.