8 Human nature is by necessity the servant of God: "The creature is a servant; we are the servants of God by nature" (St. Cyr. Alex., Thesaur. I. v., c. 5). On account, however, of original sin, our whole nature had fallen into such guilt and dishonour that we had become enemies to God. "We were by nature the children of wrath" (Eph. ii., 3). There was no power which could raise us and deliver us from this ruin and eternal destruction. But God, the Creator of mankind and infinitely merciful, did this through His only begotten Son, by whose benefit it was brought about that man was restored so that rank and dignity whence he had fallen, and was adornedwith still more abundant graces. No one can express the greatness of this workof divine grace in the souls of men. Wherefore, both in Holy Scripture and inthe writings of the fathers, men are styled regenerated, new creatures,partakers of the Divine Nature, children of God, god-like, and similar epithets.Now these great blessings are justly attributed as especially belonging to theHoly Ghost. He is "the Spirit of adoption of sons, whereby we cry: Abba,Father." He fills our hearts with the sweetness of paternal love: "TheSpirit Himself giveth testimony to our spirit that we are the sons of God"(Rom. viii., 15-16). This truth accords with the similitude observed by theAngelic Doctor between both operations of the Holy Ghost; for through Him"Christ was conceived in holiness to be by nature the Son of God," and"others are sanctified to be the sons of God by adoption" (St. Th. 3a,q. xxxii., a. I). This spiritual generation proceeds from love in a much morenoble manner than the natural: namely, from the untreated Love.
Source: Divinum Illud Munus (Vatican.va)