Isaiah 49:13 → Deuteronomy 32:43

The Song of Moses ends in a doxological summons: "Rejoice, O heavens, with Him... Rejoice, O nations, with His people" — heaven and earth conscripted to a single chorus as Yahweh avenges His servants' blood and cleanses His land and people (Deut 32:43). Isaiah 49:13 sounds the same note at the seam of the second Servant Song: "Shout for joy, O heavens; rejoice, O earth; break forth in song, O mountains! For the LORD has comforted His people, and He will have compassion on His afflicted ones." This is a sibling doxology to Isaiah 44:23 — both Isaianic refrains reach for the Song of Moses' celestial-summons-over-redemption formula: a vocative call to the heavens, paired with a corresponding summons to the earth (here amplified to the mountains), uttered as the cosmos's proper response to a decisive saving act of God. But where Isa 44:23 caps Isaiah's idol-polemic by grounding the song in redemption accomplished ("the LORD has redeemed Jacob"), Isa 49:13 follows the commissioning of the Servant as a light to the nations (49:6) and grounds the song in Yahweh's comfort (niḥam) and compassion (riḥam) on His afflicted — the same vindication-of-His-suffering-people that Deut 32:43 promises ("He will avenge the blood of His children"). This is an Echo, not a quotation: the Hebrew joy-verbs are Isaiah's own (rānnû, "shout for joy"; gîlî, "rejoice"; pitsḥû rinnâ, "break forth in song"), not the Song's wording, so the link rides the inherited gestalt rather than borrowed lexemes. The operative method is Longitudinal Theme (the canon-wide motif of all creation summoned to praise Yahweh for His redeeming deeds — Ps 96:11; 97:1; 98:4-8; Isa 44:23; 55:12), carried forward by Redemptive-Historical Progression as Moses' closing doxology becomes the native idiom of Isaiah 40–55's gospel of comfort; it is not typology, for no historical institution or person escalates into an antitype — what recurs is a doxological pattern, not a type. The road to Christ runs through that progression: the comfort over which Isaiah's heavens break into song is the shadow of the consolation that arrives in the Servant Himself (Luke 2:25, the paraklēsis of Israel), the redemption over which the angelic court Deut 32:43 first summoned at last actually worships the Lamb (Rev 5:11-13). The telos: when the veil lifts and we see that the LORD's comfort for His afflicted ones is Christ crucified and risen — the Servant who Himself bore the affliction — the summons to "break forth in song" stops being a literary refrain and becomes the only sane response of a heart that has beheld a God this glorious in saving; joining heaven's song is not duty but delight.