John Calvin 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)

Praise, O ye heavens. He now exhorts the Jews to offer thanksgiving, not only that they may testify their gratitude, but also that their own expectation of deliverance may be strengthened. Therefore, he urges believers to look upon it as an event already accomplished, as if the Lord had already delivered them.

Such modes of address make a deeper impression on our hearts than if the promises had been presented in a plain form.

Since, therefore, believers might doubt their salvation because they still languished in their miseries and were almost dead, the Prophet arouses them. He not only dictates a song to them, that they may fulfill their vows, but also shows that the word of God will be so great and uncommon that it will move heaven, earth, and the mute creatures.

Burst into praise, ye mountains. We might simply have interpreted it as “Heaven above and earth below.” However, since he mentions the “mountains,” he gives the designation of the lower parts of the earth to places that are level, such as plains and valleys, so that all countries, wherever they are situated, may be excited to praise and celebrate the name of God.

For Jehovah hath redeemed Jacob. He now adds that the work which he had aroused all to admire is the redemption of the Church, and declares that the glory of God will shine forth in it illustriously. Besides, it is proper to remember what I previously remarked: that here he not only celebrates the return of the people to their native country, but the ultimate purpose is also included. For they would be “redeemed” from the captivity in Babylon on this condition, that God should eventually collect under one head a Church taken from the whole world.