Thus it is manifest that relation really existing in God is really the same as His essence and only differs in its mode of intelligibility; as in relation is meant that regard to its opposite which is not expressed in the name of essence. Thus it is clear that in God relation and essence do not differ from each other, but are one and the same.
Reply Obj. 1: These words of Augustine do not imply that paternity or any other relation which is in God is not in its very being the same as the divine essence; but that it is not predicated under the mode of substance, as existing in Him to Whom it is applied; but as a relation. So there are said to be two predicaments only in God, since other predicaments import habitude to that of which they are spoken, both in their generic and in their specific nature; but nothing that exists in God can have any relation to that wherein it exists or of whom it is spoken, except the relation of identity; and this by reason of God's supreme simplicity.
Reply Obj. 2: As the relation which exists in creatures involves not only a regard to another, but also something absolute, so the same applies to God, yet not in the same way. What is contained in the creature above and beyond what is contained in the meaning of relation, is something else besides that relation; whereas in God there is no distinction, but both are one and the same; and this is not perfectly expressed by the word "relation," as if it were comprehended in the ordinary meaning of that term. For it was above explained (Q. 13, A. 2), in treating of the divine names, that more is contained in the perfection of the divine essence than can be signified by any name. Hence it does not follow that there exists in God anything besides relation in reality; but only in the various names imposed by us.
Reply Obj. 3: If the divine perfection contained only what is signified by relative names, it would follow that it is imperfect, being thus related to something else; as in the same way, if nothing more were contained in it than what is signified by the word "wisdom," it would not in that case be a subsistence. But as the perfection of the divine essence is greater than can be included in any name, it does not follow, if a relative term or any other name applied to God signify something imperfect, that the divine essence is in any way imperfect; for the divine essence comprehends within itself the perfection of every genus (Q. 4, A. 2). _______________________
THIRD ARTICLE [I, Q. 28, Art. 3]
Whether the Relations in God Are Really Distinguished from Each Other?
Objection 1: It would seem that the divine relations are not really distinguished from each other. For things which are identified with the same, are identified with each other. But every relation in God is really the same as the divine essence. Therefore the relations are not really distinguished from each other.
Obj. 2: Further, as paternity and filiation are by name distinguished from the divine essence, so likewise are goodness and power. But this kind of distinction does not make any real distinction of the divine goodness and power. Therefore neither does it make any real distinction of paternity and filiation.
Obj. 3: Further, in God there is no real distinction but that of origin. But one relation does not seem to arise from another. Therefore the relations are not really distinguished from each other.
On the contrary, Boethius says (De Trin.) that in God "the substance contains the unity; and relation multiplies the trinity." Therefore, if the relations were not really distinguished from each other, there would be no real trinity in God, but only an ideal trinity, which is the error of Sabellius.