Charles Ellicott 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)

The mountains and the hills ... —Cheyne aptly compares—

“Ipsi lætitia voces ad sidera jactant
Intonsi montes.” Virgil, Eclogues.

(The very hills, no longer stripped of trees,
Shall to the stars break forth in songs.)

The waving of the branches of the trees is, in the poet’s thoughts, what the clapping of hands is for people, a sign of jubilant exultation (Psalms 96:12).