False Doctrine is that which conflicts with the Word Of God and the Spirit Of God.
Since the Word Of God can be construed differently by readers it falls to the Holy Spirit to enable clear understanding of the Word.
Because many 'believers' have resisted the Holy Spirit they do not know the Spirit Of God and so are left to their own rational minds to understand the scriptures.
We worship the Lord is Spirit And Truth - not one or the other.
Abide in His Spirit and let His Word abide in you.
There are many warnings in the New Testament about False Prophets and deception.
See False Prophet and Deception for more.