The mountains skipped like rams - As flocks in their gambols. They seemed to move from place to place; everything seemed to be unsettled, and acknowledged the presence of the Omnipotent One. The word rendered "skipped" means to leap for joy; to dance. See the notes at Psalm 29:6. The reference here is to the agitations and commotions of the peaks of Sinai, when God came down to deliver the law. Exodus 19:16-18.
And the little hills like lambs - Hebrew, Like the sons of the flock. The reference here is to the less prominent eminences of Sinai. The lofty hills, and the smaller hills surrounding, seemed to be all in a state of commotion.

The (c) mountains skipped like rams, [and] the little hills like lambs.
(c) Seeing that these dead creatures felt God's power and after a sort saw it, much more his people ought to consider it, and glorify him for the same.

The mountains skipped like rams,.... The mountains of Sinai and Horeb quaked and moved at the presence of the Lord, when he descended thereon to give the law; these saw his glory and trembled, Exodus 19:18.
And the little hills like lambs; very beautiful are the larger mountains of Sinai and Horeb compared to rams, and the motion of them to their skipping; and the little hills adjacent to them to lambs: these may represent the greater and lesser governors in the Roman empire at the time when such large conversions were made in it as before observed; and which skipped, and trembled, and fled, and were moved out of their places at the downfall of Paganism and progress of Christianity, Revelation 6:14 and also may be an emblem of the difficulties which lie like mountains and hills in the way of a sinner's conversion and effectual calling, which yet give way to and are surmounted by the efficacious grace of God; all mountains become a plain before him, and when he works none can let.

skipped . . . rams-- (Psalm 29:6), describes the waving of mountain forests, poetically representing the motion of the mountains. The poetical description of the effect of God's presence on the sea and Jordan alludes to the history (Exodus 14:21; Joshua 3:14-17). Judah is put as a parallel to Israel, because of the destined, as well as real, prominence of that tribe.

The mountains - Horeb and Sinai, two tops of one mountain, and other neighbouring mountains.