I have not written unto you because ye know not the truth, but because ye know it, and that no lie is of the truth.
Because ye know it, and that ... Ye not only know the truth (concerning the Son and the Father, 1 John 2:13), but else can detect a lie as opposed to the truth. For right is index of itself and of what is crooked (Estius). Alford, 'Because ye know it, and because no he is of the truth' ('every lie excluded from being of the truth'), I therefore wrote (in this letter) to point out the lie and the liars.