1 John 2:21

I have not written, etc. - It is not because ye are ignorant of these things that I write to you, but because you know them, and can by these judge of the doctrines of those false teachers, and clearly perceive that they are liars; for they contradict the truth which ye have already received, and consequently their doctrine is a lie, and no lie can be of the truth, i.e. consistent with Christianity.