Essential doctrines are those core teachings that distinguish Christians from non-Christians and must be believed in order for one to be a genuine follower of Christ.
Christians frequently disagree about various non-essential teachings, but disagreement about these doctrines does not amount to a denial of the faith. In other words, those who disagree on matters that are not absolutely essential to the faith, while affirming core doctrines, have in no way ceased to be genuine brothers and sisters in Christ.
Romans 14:1, 4, 12, 22; 1 Corinthians 10:23-24