Is 12:5-6, “Sing praises to YHWH, for He has done gloriously; let this be made known in all the earth. Shout and sing for joy, O inhabitant of Zion, for great in your midst is the Holy One of Israel.”
Isaiah envisions a day when the joyful praises of YHWH’s redeemed people will fill the earth with the witness of what He has done (“for He has done gloriously”). When we read Isaiah 12 in conjunction with Isaiah 11, it becomes clear that the filling of the earth with the witness to YHWH’s saving WORK is synonymous with the filling of the earth with the knowledge of YHWH’s glorious NAME (11:9, 12:4), which is to say, with the Beauty of His Identity, the Excellence of Who He Is.
What is this work that YHWH has done which causes His people to sing for joy and by which His Name is made known in all the earth? It must have something to do with the final sentence of this passage: “great in your midst is the Holy One of Israel.” The work that YHWH has done—the work that fills His people with joy, the work that is proclaimed among the nations such that His Name / Identity / Character fills all the earth—that work is bound up with the idea of YHWH manifest as “great” in the midst of His people. So, what is this greatness of the Lord in the midst of His people?
I believe we find an answer when we look at this passage in the Greek OT. There the word translated “great” is “ὑψόω” or “lifted up,” such that the passage might be translated: “Shout and sing for joy, O inhabitants of Zion, for LIFTED UP in your midst is the Holy One of Israel.”
Why is that significant? Because “lifted up” is the phrase that John picks up from Isaiah and uses to speak of the crucifixion (Jn 3:14, 8:28, 12:32). It is precisely as Jesus is lifted up on the cross that He is revealed to the seeing eye as the Holy One of Israel, great and glorious in the midst of His people. THIS, then—the lifting up of the incarnate Son on the cross of His suffering which, when viewed in light of His having been lifted up from the grave, is the throne of YHWH’s majesty—THIS is the great work of YHWH, of which His people sing, in which His Bride rejoices, and by which His Name is made known in all the earth.