FIGLIO DI DIO
This term, in common usage, can denote every creature insofar as it is produced by God and watched over by His providence; or the rational creature insofar as, through grace, it is destined to enjoy God in beatific vision ("adoptive son"); or finally, the natural Son of God, He who proceeds from God the Father through generation, from whom He is therefore truly distinct, even though He shares the same divine nature. In this sense the term must be understood when speaking of the Son of God as the second Person of the Holy Trinity. Thus was it defined at the Council of Nicaea (325) against the heresy of Arius, who maintained that the Word, that is, the Son of God, was the first and most exalted creature of God (v. CONSOSTANZIALE).
The doctrine of the Church, already intimated in the Old Testament, appears with full clarity in the books of the New Testament, where the Son of God is revealed "in the person of Jesus Christ." He is indeed qualified as the natural Son of God (Rom. 8:32), the only Son (Matt. 3:17; 17:5), the Only Begotten (John 1:14, 18; 3:16), the Firstborn (Col. 1:15), the true Son (John 5:20); titles which absolutely exclude any sonship other than the natural.
Jesus Christ Himself always speaks of God as His Father and as the Father of men, but He makes it clear that He is His Father in a wholly special and exclusive way, for He always distinguishes the divine paternity toward Himself from that toward men ("My Father, your Father": cf. Luke 22:29; Matt. 10:33; 6:32; 10:20, 17). If our relationship with God is one of adoptive sons, Christ’s is one of natural sonship; a fact which is further evident from those testimonies in which Christ affirms equality with the Father in power, will, and nature (John 5:17–27; 16:15; 10:30). Thus did both His friends, such as Peter (Matt. 16:16), and His enemies, such as the Sanhedrin (Matt. 26:63 sq.), interpret the thought of Christ.
If Christ is the natural Son of God, we must admit within the Godhead an act of generation, whereby the divine life flows from God the Father, who begets, to God the Son, who is begotten: an eternal and necessary generation, as all in God is eternal and necessary; of a spiritual order, because God is pure spirit. This resolves into a simple origin of the Son from the Father, which does not entail any productive action, for the Son is uncaused, unbegotten. Yet for generation to occur, the origin must be founded upon an operation, which exists of a nature such that the proceeding One is of the same living substance as the principle from which He proceeds. It has been inquired what this operation might be, and it has been unanimously answered that it is identified with the intellectual knowledge of God. Even Sacred Scripture, presenting to us the Son of God as the Word (Prologue of the Gospel of John), as the living Image and radiance of the Father (Col. 1:15–19; Heb. 1:3), leads us to think that He proceeds by way of intelligence. But theological inquiry, pressing further, affirms that the Son of God is Son because He is the Word, because He proceeds by reason of intellectual knowledge. Unlike any other intelligence, even a created one, the Word is by its nature similar to the object known, of which it is the faithful representation. In God, however, in whom knowledge has as its object the divine nature, the Word is necessarily similar to the divine nature; for in God there can be nothing accidental, and such similarity is necessarily substantial. Therefore the Word proceeds as a living God from a living God, drawing its consubstantiality from the very fact that it proceeds as Word, that is, by way of intelligence. Therefore the Word is the Son of God, and is the Son of God because He is the Word.
Yet every attempt of reason to sound the secret of God’s intimate life must at a certain point come to a halt in a further act of faith before the depths of the mystery, whose direct knowledge is reserved for the beatific vision (v. PARADISO).