All then that the Son and the Spirit have is from the Father, even their very being: and unless the Father is, neither the Son nor the Spirit is. And unless the Father possesses a certain attribute, neither the Son nor the Spirit possesses it: and through the Father, that is, because of the Father's existence, the Son and the Spirit exist, and through the Father, that is, because of the Father having the qualities, the Son and the Spirit have all their qualities, those of being unbegotten, and of birth and of procession being excepted. For in these hypostatic or personal properties alone do the three holy subsistences differ from each other, being indivisibly divided not by essence but by the distinguishing mark of their proper and peculiar subsistence.
St. John Damascene, Exposition of the Orthodox Faith, Book I, Chapter VIII
