from part of a comment 69
http://www.calledtocommunion.com/2010/04/catholic-and-reformed-conceptions-of-the-atonement/
In the Creed, we begin by saying we believe in one God, and in this way we rule out polytheism. But we also say of Jesus Christ that He is “born of the Father before all ages. God from God, Light from Light, true God from true God, begotten, not made, consubstantial with the Father;” and in saying “begotten, not made” we rule out Arianism. But the difference between ‘begotten’ and ‘made’ is that ‘begotten’ is eternal, necessary and internal to God, whereas ‘made’ is temporal, contingent, and external to God, in the sense that nothing made is consubstantial with the Father, whereas the Son and the Spirit are consubstantial with the Father. They are consubstantial with the Father, and yet the Son is not the Father, and the Spirit is not the Father, only because they are internal processions of the Father. That’s what “eternally begotten” of the Father means, in the case of the Son, and “proceeding from the Father and the Son” means, in the case of the Spirit.
So the Tradition preserved in the Creed teaches that the Son is internal to the Father, not external. He is the Father’s internal, eternal, Word, the perfect Concept of the Father, that is, the Father’s own internal Concept. The Father has no other internal Word, no other internal Concept. It is not as though the Father can reject His own internal Word, His own internal Concept. That would turn God the Father into a zombie, with no internal Word, no self-understanding, no ‘lights on inside.’ The very notion is blasphemous. The Father cannot lose fellowship with Himself, and therefore He cannot lose fellowship with His own perfect internal Word, because fellowship with His perfect internal Word is His perfect fellowship with Himself. Likewise, the Son is “the power of God and the wisdom of God” (1 Cor 1:24). The Father has no other Power than the Son, no other Wisdom than the Son. That is why without Him [i.e. the Logos], nothing was made that has been made. (John 1:3) The Father made the heavens and the earth by His Wisdom, His Understanding. (Jer. 10:12, 51:15) And that Wisdom and Understanding is the Logos, the Second Person of the Trinity. The Father cannot reject or break fellowship with His own Power and Wisdom and Understanding; that would leave Him [i.e. the Father] powerless and witless. Again, the very idea is blasphemous. The Logos is the definitive Word of God because the Father has no other Word. If the Father had another Word, then Christ would not be the Father’s “one, perfect and unsurpassable Word.” It would not be true that “In him he has said everything; there will be no other word than this one.” (Catechism of the Catholic Church, 65) But the notion that the Father could break the ancient, eternal fellowship with the Son, without losing His self-understanding, requires that the Father have a second Logos by which the Father retains self-understanding, even while estranged from the first Logos.
