Charles Ellicott Commentary Deuteronomy 32:43

"Rejoice, O ye nations, [with] his people: For he will avenge the blood of his servants, And will render vengeance to his adversaries, And will make expiation for his land, for his people." — Deuteronomy 32:43 (ASV)

Rejoice, O you nations, with his people.—This is cited by Paul to show that the Gentiles must also glorify God for His mercy in sending Jesus Christ. But it is not wholly fulfilled yet. If the fall of God’s people was the wealth of the world ... what will the receiving of them be, but life from the dead? (Romans 11:15; Romans 15:10).

The Septuagint has a longer version of this verse, Rejoice, you heavens, with Him, and let all the angels of God worship Him (Hebrews 1:7); Rejoice, you Gentiles, with His people, and let all the sons of God be strong in Him; for, etc.

And will be merciful unto.—Literally, will reconcile or make atonement for His land, the land of His people, or for the land of His people. He will cleanse, forgive, and be merciful to it. The very last words speak of local restoration of the land to the people, and the people to the land. Of no other land has He said, “The land is mine.” “Israel” alone is called His “firstborn.”