The Essentials – Part 1

What doctrines are absolutely essential to Christianity?  As the Word of God, all Scripture is equally and absolutely authoritative.  But not all Scripture is equally clear, nor equally central to salvation.  Christians disagree on certain nuanced details, yet are united by our common salvation by God’s grace through faith in Christ.  On the other hand, there are people who profess to be Christians, but who deny central, core doctrines of the faith.  Where is the line that divides genuine faith from a false faith?  At what point does theological error become heresy?