We have different doctrines in Christianity because of the belief of the founder of each denominations. The things they believe according to their interpretation of the scripture are what they inject into their members that forms a big congregation.
There are list of doctrines in Christianity which is seen from different perspectives by different churches. For example, Holy ghost baptism, Redemption, Justification, water baptism and so on.
All these are found in the bible but the way its understood by different churches is what causes the differences in doctrines.
Some churches will stand on the fact that there is no hell and they will back it with scriptures. Another will bring out a verse in the bible that shows that hell exists.
Now which one will you believe as a christian?
That is why Doctrine is defined as a belief that is taught according to the way its understood.
Another instance: some churches believe in baptizing through sprinkling (Aspersion) of water while another believes in total immersion of the body.
They both call it baptism but its done in different way due to their belief.
Most doctrines are seen in the bible and followed according to the understanding of the reader.
Virtually all christian doctrines have biblical basis
Ezekiel 36:25-26. " I will sprinkle clean water on you, and you will become clean; I will cleanse you from all your uncleanness and from all your disgusting idols. 26 I will give you a new heart and put a new spirit inside you. I will take the heart of stone out of your flesh and give you a hear of flesh.
This scripture shows that the sprinkling type of baptism was taken from the bible
Mark 1 :4-5". And so John the Baptist appeared in the wilderness, preaching a baptism of repentance for the forgiveness of sins. 5 The whole Judean countryside and all the people of Jerusalem went out to him. Confessing their sins, they were baptized by him in the Jordan River.
Act 8 :36-38". As they traveled along the road, they came to some water and the eunuch said, “Look, here is water. What can stand in the way of my being baptized? ” 38 And he gave orders to stop the chariot. Then both Philip and the eunuch went down into the water and Philip baptized him. 39 When they came up out of the water, the Spirit of the Lord suddenly took Philip away, and the eunuch did not see him again, but went on his way rejoicing.
These verses also holds some points for baptism by immersion.
All the different doctrines portrayed by churches are picked from the bible and their belief are tied to their interpretation of the scripture.
As long as the main doctrines that gave birth to Christianity (the diety of Christ,The crucification, the resurrection of Christ and salvation by grace) is still intact,we can all remain as one church.