The spiritual source of all false doctrine are demons - 1 Tim. 4:1. However, the practical sources of false doctrine can be summarized by two categories: 1. Source of authority external to Scriptures 2. Failure to properly interpet a given text by its immediate context. There are many on this forum that fall in the second category. Instead of careful exegesis of a text in its immediate context they read into that text and context scriptures outside that context. The scriptues they use to read into another context usually are not properly interpreted by their own immediate context, and so they duplicate their error twice over when they use a proof text out of context to interpet another text in a different context. This is the repeated and common error that I run into with many on this forum. This is the root of most false doctrine - trying to interpret a text by using proof texts out of context. THE PROPER PROCEDURE: The proper procedure is first interpet a text or word by its immediate context. ONce that is established then proceed to deal with other texts that might have an appearance of contradiction by interpreting them first by their own immediate context. Usually, the appearance of contradiction is removed by proper exegesis of that proof text in its own context. Hence, don't jump from text to text or attempt to read other texts into a certain context until you first have established the contextual interpetation. If this basic procedure is not followed there is no end of error and no way for scriptures to be properly harmonized.