Tertullian · a new plain-English translation from the original language
[1] But this — believing in one God in such a way that you refuse to count the Son alongside him, and after the Son, the Spirit — is a piece of Jewish faith. What, after all, would be left to distinguish us from them, except just this difference? What would be the point of the gospel, what the substance of the New Testament establishing the Law and the Prophets "up to John," if the Father, Son, and Spirit are not, from that point forward, believed as three yet reckoned one God? [2] This is why God willed to renew the covenant: so that he might now be believed as one in a new way, through the Son and the Spirit, so that God might at last be known openly under his own proper names and persons — the very God who, previously proclaimed through the Son and Spirit, was not understood. [3] Let the antichrists take note, then, who deny Father and Son alike: they deny the Father by naming him the Son, and deny the Son by supposing him the Father, crediting each with what he is not and stripping each of what he is. But whoever confesses Christ as God's Son, and not as the Father, has God dwelling within, and dwells in God himself. We trust the witness God has borne about his Son: "Whoever does not have the Son does not have life either." And he does not have the Son who believes him to be someone other than the Son.