According to its inscription, Psalm 72 is in praise of Solomon, for his mercy, piety, and might. Towards the end, the psalmist exclaims, “May men bless themselves (יִתְבָּרְכוּ) by him, all nations (גֹּויִם) call him blessed!” (Ps 72:17, RSV) This has first-blush resonances with the LORD’s promise to Abraham, “In thee shall all families (מִשְׁפְּחֹת) of the earth be blessed (נִבְרְכוּ)” (Gen 12:3, KJV). Nonetheless, there are some important differences — the psalm mentions “nations” rather than “families,” and it conjugates the verb barach in the reflexive Hithpael binyan rather than in Genesis’s passive Niphil.
That’s why it’s doubly striking to compare the verses in the LXX. Here, the Psalm reads: “εὐλογηθήσονται ἐν αὐτῷ πᾶσαι αἱ φυλαὶ τῆς γῆς πάντα τὰ ἔθνη μακαριοῦσιν αὐτόν” (Ps 72:16, LXX). Except for the necessary revision of the pronoun, this is identical to Genesis 12: “ἐνευλογηθήσονται ἐν σοὶ πᾶσαι αἱ φυλαὶ τῆς γῆς” (Gen 12:3, LXX). Whoever translated this Old Greek version of the Psalm, presumably with the Pentateuchal LXX before him, seems to have deliberately brought it into conformity with the LORD’s promise to Abraham. The promise that Israel would be a blessing to all nations is now to be fulfilled in the reign of a Davidic king.
Which means that these promises were already being interlaced, brought together under some kind of hermeneutical pressure, long before Paul proclaimed that the promise to Abraham had in fact been fulfilled in David’s true heir (cf. Gal 3:8, Rom 1:3).