Jenson (Systematic Theology: Volume 1: The Triune God, 108-9) refers to Thomas’s definition of persona as “a relation in the mode of substance” (ST 1, 29, 4) and asks, “How does this work within the narrated reality itself?” His answer is a tightly-packed little bomb:
“It is exactly in that Jesus of his Father or the Spirit refers absolutely from himself to one of the others as the one God that he is in a specific way a perfect correlate to that other, and so himself God within and of the history plotted by these referrals.” There’s more, but let’s take a breath. The point is that each person refers away from Himself to another. The Son glorifies the Father, the Father the Son, the Spirit honors the Son who honors the Father. In that “absolute” referral-away, the referring Person is a perfect correlate to the other: In the Son’s referring to the Father as the one God, the Son is the correlate of the Father in a specifically filial way; in the Spirit’s referring from Himself to the Son, He is the correlate of the Son, the Spirit of the Son. As each absolutely refers away, He doesn’t just acknowledge the referred-to as God, but, as correlate, establishes His own divinity in correspondence to the other.
Referring to John’s gospel, Jenson notes that “Jesus turns aside all attributions to himself of what belongs to the Father, even as his teaching and action apparently call for them. Just so Jesus is the perfect counterpart to the Father, that is, ‘the Son,’ and the perfect Word of the Father; and so is himself the eternal possessor of deity.” Similarly, “Of the Father it is said that the Father has turned over the role of God to the Son [citing John 5:23; 17:2, 6]. To be related to God we are therefore directed not to the Father but to the Son.” In this Jenson sees the Athanasian and Cappadocian claim that “it is by intending the Son as God that the Father is God.”
Having laid that ground, Jenson uses it to drive out the last vestiges of subodinationism: “If only the Son and the Spirit could be so described, it could still be thought that being correlated in this way to God did not amount to being God as the Father is; but since the Father figures in this same way in the triune story, there is no other form of Godhead to be superior.” If, in other words, the Father were only the “referred-to” and not one also “referring-away,” it would appear that the Persons “referring-away” were not so much God as the Father is. There is, however, a completely mutual reference and correlation, and so each is wholly God, distinguished in the specific manner of His referring-away from Himself to the others.