Sing, O ye heavens. The sympathy of external nature with the fortunes of Israel is assumed throughout Isaiah, as it is throughout the Psalms (see Psalms 11:6 -8; Psalms 24:4-7; Psalms 29:1-11:17; 30:25, 26; Psalms 33:9; Psalms 35:1, Psalms 35:2, Psalms 35:7, etc.
). If Israel is depressed, the earth must "mourn and languish," the heavens grow dark; the mountains shrink and "be ashamed." If, on the contrary, Israel prospers, heaven and earth, mountain and forest, must alike rejoice and sing.
Dr. Kay expounds the rejoicing of the heavens here (and also in Isaiah 49:13),of the joy felt by the angels over the returning and pardoned sinner; but the context of both passages is in favour of the material heavens being meant.
It is quite possible that there is a real and not merely a fancied sympathy between the material and the spiritual worlds. The Lord hath done it; literally, the Lord hath wrought—what he has wrought is not said.
Mr. Cheyne translates, "Jehovah hath done nobly." Shout, ye lower parts of the earth. Metonymy of the part for the whole—"the lower parts of the earth" for "the earth even to its lowest depths." There is no thought of Sheol or of its inhabitants.
Break forth into singing (comp. Isaiah 14:7; Isaiah 35:2). As children and birds sing from the very gladness of their hearts, thereby venting the joy that almost oppresses them, so all nature is called upon, not merely to rejoice, but to give vent to its joy, now that Israel is redeemed and God glorified.