Objection 1. It would seem that this name "Father" is not applied to God, firstly as a personal name. For in the intellect the common precedes the particular. But this name "Father" as a personal name, belongs to the person of the Father; and taken in an essential sense it is common to the whole Trinity; for we say "Our Father" to the whole Trinity. Therefore "Father" comes first as an essential name before its personal sense.
Objection 2. Further, in things of which the concept is the same there is no priority of predication. But paternity and filiation seem to be of the same nature, according as a divine person is Father of the Son, and the whole Trinity is our Father, or the creature's; since, according to Basil (Hom. xv, De Fide), to receive is common to the creature and to the Son. Therefore "Father" in God is not taken as an essential name before it is taken personally.
Objection 3. Further, it is not possible to compare things which have not a common concept. But the Son is compared to the creature by reason of filiation or generation, according to Colossians 1:15: "Who is the image of the invisible God, the first-born of every creature." Therefore paternity taken in a personal sense is not prior to, but has the same concept as, paternity taken essentially.
On the contrary, The eternal comes before the temporal. But God is the Father of the Son from eternity; while He is the Father of the creature in time. Therefore paternity in God is taken in a personal sense as regards the Son, before it is so taken as regards the creature.
I answer that, A name is applied to that wherein is perfectly contained its whole signification, before it is applied to that which only partially contains it; for the latter bears the name by reason of a kind of similitude to that which answers perfectly to the signification of the name; since all imperfect things are taken from perfect things. Hence this name "lion" is applied first to the animal containing the whole nature of a lion, and which is properly so called, before it is applied to a man who shows something of a lion's nature, as courage, or strength, or the like; and of whom it is said by way of similitude.
Now it is manifest from the foregoing (27, 2; 28, 4), that the perfect idea of paternity and filiation is to be found in God the Father, and in God the Son, because one is the nature and glory of the Father and the Son. But in the creature, filiation is found in relation to God, not in a perfect manner, since the Creator and the creature have not the same nature; but by way of a certain likeness, which is the more perfect the nearer we approach to the true idea of filiation. For God is called the Father of some creatures, by reason only of a trace, for instance of irrational creatures, according to Job 38:28: "Who is the father of the rain? or who begot the drops of dew?" Of some, namely, the rational creature (He is the Father), by reason of the likeness of His image, according to Deuteronomy 32:6: "Is He not thy Father, who possessed, and made, and created thee?" And of others He is the Father by similitude of grace, and these are also called adoptive sons, as ordained to the heritage of eternal glory by the gift of grace which they have received, according to Romans 8:16-17: "The Spirit Himself gives testimony to our spirit that we are the sons of God; and if sons, heirs also." Lastly, He is the Father of others by similitude of glory, forasmuch as they have obtained possession of the heritage of glory, according to Romans 5:2: "We glory in the hope of the glory of the sons of God." Therefore it is plain that "paternity" is applied to God first, as importing regard of one Person to another Person, before it imports the regard of God to creatures.
Reply to Objection 1. Common terms taken absolutely, in the order of our intelligence, come before proper terms; because they are included in the understanding of proper terms; but not conversely. For in the concept of the person of the Father, God is understood; but not conversely. But common terms which import relation to the creature come after proper terms which import personal relations; because the person proceeding in God proceeds as the principle of the production of creatures. For as the word conceived in the mind of the artist is first understood to proceed from the artist before the thing designed, which is produced in likeness to the word conceived in the artist's mind; so the Son proceeds from the Father before the creature, to which the name of filiation is applied as it participates in the likeness of the Son, as is clear from the words of Romans 8:29: "Whom He foreknew and predestined to be made conformable to the image of His Son."
Reply to Objection 2. To "receive" is said to be common to the creature and to the Son not in a univocal sense, but according to a certain remote similitude whereby He is called the First Born of creatures. Hence the authority quoted subjoins: "That He may be the First Born among many brethren," after saying that some were conformed to the image of the Son of God. But the Son of God possesses a position of singularity above others, in having by nature what He receives, as Basil also declares (Hom. xv De Fide); hence He is called the only begotten (John 1:18): "The only begotten Who is in the bosom of the Father, He hath declared unto us."
From this appears the Reply to the Third Objection.
Source: Summa Theologica (New Advent)