John Gill Bible Commentary

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, Exo 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, Rev 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.