12. What, then, could have been said to signify more expressly the unity of the Godhead, or of Its working, which Unity is according to the Godhead of the Father, or of the Son, or of the Holy Spirit, than that we should understand that the fulness of the eternal Godhead would seem to be divided far more than this body of ours, if any one were to sever the unity of Substance, and multiply Its powers, whereas the eternity of the same Godhead is one?
Complete source paragraph · On the Holy Spirit, Chapter III., source paragraph 4 · Original source