False doctrine – anything claiming to be the truth that is in fact a lie.
False teachers typically claim to have the superior knowledge (as in gnosticism). They claim to know the transcendent secrets, but actually are ignorant and infantile in their understanding.
Paul identifies 3 characteristics of false teachers: 1) they “teach otherwise” – a different doctrine, or any teaching that contradicts God’s revelation in Scripture; 2) they do “not consent to wholesome words” – they do not agree with sound, healthy teaching, specifically the teaching contained in Scripture; and 3) they reject “doctrine which accords with godliness” – teaching not based on Scripture will always result in an unholy life. Instead of godliness, false teachers will be marked by sin.
Commentary from the MacArthur Study Bible, notes for 1 Timothy 6:3, 6:20.