"The sacrosanct Roman Church, founded by the voice of our Lord and Savior, firmly believes, professes, and preaches one true God omnipotent, unchangeable, and eternal, Father, Son, and Holy Ghost; one in essence, three in persons; Father unborn, Son born of the Father, Holy Spirit proceeding from Father and Son; that the Father is not Son or Holy Spirit, that Son is not Father or Holy Spirit; that Holy Spirit is not Father or Son; but Father alone is Father, Son alone is Son, Holy Spirit alone is Holy Spirit. The Father alone begot the Son of His own substance; the Son alone was begotten of the Father alone; the Holy Spirit alone proceeds at the same time from the Father and Son. These three persons are one God, and not three gods, because the three have one substance, one essence, one nature, one divinity, one immensity, one eternity, where no opposition of relationship interferes.
“Because of this unity the Father is entire in the Son, entire in the Holy Spirit; the Son is entire in the Father, entire in the Holy Spirit, the Holy Spirit is entire in the Father, entire in the Son. No one either excels another in eternity, or exceeds in magnitude, or is superior in power. For the fact that the Son is of the Father is eternal and without beginning; and that the Holy Spirit proceeds from the Father and the Son is eternal and without beginning.” Whatever the Father is or has, He does not have from another, but from Himself; and He is the principle without principle. Whatever the Son is or has, He has from the Father, and is the principle from a principle. Whatever the Holy Spirit is or has, He has simultaneously from the Father and the Son. But the Father and the Son are not two principles of the Holy Spirit, but one principle, just as the Father and the Son and the Holy Spirit are not three principles of the creature, but one principle."
(Council of Florence)
The problem is that although you use biblical language, you wish to derive non-biblical thoughts from it. From the expression 'Son of God,' you want to deduce that the Son is not God, although it does not mean that. One should just understand the expression "Son of God." When we say 'Son of God' referring to Jesus, it answers the question of who he is, and the statement that he is 'God' answers the question of what he is. It is entirely clear that a person whose father is God will himself be God. Just as the son of man is man, and the foal of a horse is a horse.
There are three senses in which someone can be "Son of God." In the broadest sense, every human is a child of God, that is, a creation of God's providential care. In a more narrow sense, sonship to God means being the possessor of supernatural grace, of supernatural rebirth in God, which comes about when God no longer regards us as servants, but as adopted sons. In the narrowest sense, "Son of God" refers to the second divine person, who in some way beyond our comprehension has been "begotten" by the Father from eternity, proceeds, emanates from Him; but in such a way that they are one in being, essence, one God. That Jesus was the Son of God in this last sense has been shown above. This sonship is expressed in Scripture as talking about the "only begotten Son," while we humans can only be God's adopted sons, metaphorically speaking, his children. Jesus himself feels a different relationship with the Father than we do; he never says, for example, "our Father," but rather "my Father and your Father." He is the "only begotten Son," who is "in the bosom of the Father." (John 1:18).
In Jewish tradition, a son inherited his father's name, title, and social position. If Jesus inherited the Father's power, rights, and especially His name, then this means that Jesus is the Almighty God. Jesus confirmed this himself.
The Bible calls angels "sons of God" (Hebrew b'né Elohim) (Job 38:7, Psalm 36:9) and collectively refers to Judaism, the whole nation, as God's "son" (Hos 11:1). At the same time, no Jew could personally call God his own father, as if he were directly descended from God Himself, because this would have made him God as well (cf. Jn 10:33).
Jesus referred to himself with two specific expressions: he is the "Son of God" and the "Son of Man." The "son of ...." structure, like in other languages, mostly expresses a genealogical relationship in Hebrew (e.g., Jonah's son, Simon), but it is also a unique grammatical phenomenon in Hebrew that does not relate but qualifies, for example, the "sons of disobedience" (Eph 2:2) are those who are disobedient, as the "son of death" is dead.
Firstly, therefore, when Jesus declared himself to be "the Son of Man" (Mt 16:13), it primarily means: "who is Man." Secondly, this expression is a figure from an Old Testament apocalyptic vision, one who "sits at the right hand of the Mighty One," and who, returning to earth, will be the king of the nations (Dan 7:13-14 cf. Mt 26:63-66, 25:31). From the reactions, it is clear that Jesus' contemporaries understood precisely the kind of authority Jesus claimed for himself with the title Son of Man.
On the other hand, Jesus also declared himself to be "the Son of God," which means: "who is God." In terms of his relationship with the Father, he is God's only Son (Jn 3:16; "only begotten" = unique), therefore he is the Son (1Jn 1:3, 2:22-24, 3:17, 4:9,14, 5:12, etc.), to whom God personally is His own Father (Mt 11:27, Lk 10:22, Jn 10:32-38), through whom the Father teaches and acts (Jn 14:10-11). As he said: "all that the Father has is mine" (Jn 16:15), since "I and the Father are one" (Jn 10:30). Jews understood Jesus' self-proclamations as making himself "God, being a man" (Jn 10:33), because his words could not be understood differently with an Old Testament and Hebrew ear.
It is noteworthy that, according to the New Testament, believers are also "sons of God" (Gal 3:27), but while the Son is inherently, eternally God by his own nature, believers become partakers of His divine nature – in character, immortality, glory – through God's grace (2Pt 1:4, 2Cor 3:18, 1Jn 3:2, 1Cor 15:53-54).
From the idea of "sonship" here, we naturally must distance ourselves from any notion derived from human life according to which the father exists first, and only after some time does the son come into being, which means the father is greater, stronger, wiser, and in comparison, the son is for a long time entirely subordinate. Instead, we should consider what "sonship" meant in the context of ancient Eastern patriarchal conditions, where in the son, the entire household could see the father's alter ego, the heir to all his possessions, a sharer in all his authority. And we can think of the often-occurring phenomenon where the adult son often indeed appears as a carbon copy of the father. The same facial features, the same movements, the same way of speaking and thinking, as if the father lives a second life through the son. When the Father is God, not at a certain point in time, but from eternity to eternity, He pours out the life of the Son of God from Himself, in that He can contemplate a mirror image of His own being, and He projects His true likeness before us so that we may know Him from it. The Son is the same God but in a different manner: in the form of God revealing Himself. The Bible expresses this clearly and aptly when it refers to the Son with a different designation as the "Word," which – or rather who – was "with God" from eternity, and "was God." The Son of God is thus the living God in His articulation, the eternal Word, in which God expresses Himself.
