The Monarchy of the Father

The Father alone is the source. The Son is begotten of Him and the Spirit proceeds from Him, and neither is begotten or proceeds from the divine essence as such, or from the Son. This is what the Greek Fathers mean by saying the Church confesses one God because it confesses one Father: the unity of the Trinity is secured by a Person, not by a shared substance standing behind the three. St Gregory the Theologian says the three are one in nature and that the union is the Father, from whom and to whom the others are referred. Without this the argument against the Filioque is only half made, because the objection is not that the Spirit has too many sources but that giving Him two destroys the one He has.