“Children, it is the last hour: and as you have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last hour. They went out from us, but they were not of us: if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us. But you have an unction from the Holy One, and know all things. I write unto you, not because you know not the truth, but because you know it, and that no lie is of the truth.
Who is a liar but he that denies that Jesus is the Christ? [He is antichrist, that denies the Father and the Son.] Whosoever denies the Son, the same has neither the Father nor the Son: and he that acknowledges the Son has both the Father and the Son. Let that therefore abide in you, which you have heard from the beginning. If that which you have heard from the beginning shall remain in you, you also shall continue in the Son, and in the Father. And this is the promise that He has promised us, even eternal life. These things have I written unto you concerning them that seduce you; that you may know that you have an unction, and that the unction which you have received of him may abide in you. And you need not that any man teach you; because His unction teaches you of all things.”
Source: Homilies on the First Epistle of John (New Advent)