The Bible itself reveals those doctrines that are essential to the Christian faith. They are 1) the Deity of Christ, 2) Salvation by Grace, 3) Resurrection of Christ, 4) the gospel, and 5) monotheism. These are the doctrines the Bible says are necessary.
This small article could very well determine whether you are in or out of the Christian Faith
Litmus Test: You have to believe items 1-5 to be in the Christian Faith.