1 John 2:19-22

They went out from us [seeming at first to be Christians], but they were not really of us [because they were not truly born again and spiritually transformed]; for if they had been of us, they would have remained with us; but they went out [teaching false doctrine], so that it would be clearly shown that none of them are of us. But you have an anointing from the Holy One [you have been set apart, specially gifted and prepared by the Holy Spirit], and all of you know [the truth because He teaches us, illuminates our minds, and guards us from error]. I have not written to you because you do not know the truth, but because you do know it, and because no lie [nothing false, no deception] is of the truth. Who is the liar but the one who denies that Jesus is the Christ (the Messiah, the Anointed)? This is the antichrist [the enemy and antagonist of Christ], the one who denies and consistently refuses to acknowledge the Father and the Son.