Charles Ellicott Commentary Isaiah 44:23

"Sing, O ye heavens, for Jehovah hath done it; shout, ye lower parts of the earth; break forth into singing, ye mountains, O forest, and every tree therein: for Jehovah hath redeemed Jacob, and will glorify himself in Israel." — Isaiah 44:23 (ASV)

The Lord hath done it. —The pronoun supplied in the Authorized Version refers to the redemption of Isaiah 44:22; but the word may be taken absolutely in the sense has done mightily.

Ye lower parts of the earth. —These, as in Ephesians 4:9, are equivalent to Sheol, or Hades. Even they, commonly thought of as echoing no song of praise (Psalms 6:5; Psalms 88:12; Isaiah 38:18), are invited to join in the great doxology.