8 All, therefore, are outside of the [Christian] dispensation, who, under pretext of knowledge, understand that Jesus was one, and Christ another, and the Only-begotten another, from whom again is the Word, and that the Saviour is another, whom these disciples of error allege to be a production of those who were made Æons in a state of degeneracy. Such men are to outward appearance sheep; for they appear to be like us, by what they say in public, repeating the same words as we do; but inwardly they are wolves.
Their doctrine is homicidal, conjuring up, as it does, a number of gods, and simulating many Fathers, but lowering and dividing the Son of God in many ways. These are they against whom the Lord has cautioned us beforehand; and His disciple, in his Epistle already mentioned, commands us to avoid them, when he says: “For many deceivers are entered into the world, who confess not that Jesus Christ has come in the flesh. This is a deceiver and an antichrist. Take heed to them, that you lose not what you have wrought.” And again does he say in the Epistle: “Many false prophets are gone out into the world.
Hereby know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is of God; and every spirit which separates Jesus Christ is not of God, but is of antichrist.” These words agree with what was said in the Gospel, that “the Word was made flesh, and dwelt among us.” Wherefore he again exclaims in his Epistle, “Every one that believes that Jesus is the Christ, has been born of God;” knowing Jesus Christ to be one and the same, to whom the gates of heaven were opened, because of His taking upon Him flesh: who shall also come in the same flesh in which He suffered, revealing the glory of the Father.
Source: Adversus haereses (New Advent)