John Calvin Commentary Isaiah 55:12

"For ye shall go out with joy, and be led forth with peace: the mountains and the hills shall break forth before you into singing; and all the trees of the fields shall clap their hands." — Isaiah 55:12 (ASV)

Therefore ye shall go out with joy. The Prophet concludes the subject of this chapter. For when he spoke of the mercy of God, his object was to convince the Jews that the Lord would deliver them. He now applies to his purpose what was contained in his discourse concerning the infinite goodness of God, and shows that his thoughts are very unlike the thoughts of men. And the true way of teaching is this: that we should apply general statements for present use. Finally, he addresses the restoration of the people, which depended on the undeserved mercy of God.

The mountains and hills shall break out before you. By “the mountains and hills” he means that everything they will meet in the journey, though in other respects it may be harmful, will aid those who will return to Jerusalem. They are metaphors, by which he shows that all the creatures bow to the will of God, and rejoice and lend their aid to carry on his work.

He alludes to the deliverance from Egypt (Exodus 14:22), as is customary with the Prophets. For this is how it is described by the Psalmist: The mountains leaped like rams, and the hills like lambs. What ailed thee, O sea, that thou fleddest, and Jordan, (Joshua 3:16) that thou wast driven back? (Psalms 114:4, 5).

For the restoration of the Church may be regarded as a renovation of the whole world, and in consequence of this, heaven and earth are said to be changed, as if their order were reversed. But all this depended on former predictions, by which they had received a promise of their return.