Share 'Salvific issues?'

I know that "we" throw around terms like heretic, and false teacher and such when someone adheres to a doctrine different than ours - but I wonder, what does the Bible teach about salvific issues? How much doctrine can you get wrong, and still be saved? Is there a difference between the thief on the cross, who was saved with no more doctrine than "You are the Christ" and those who have more kno...