Bow thy heavens, O LORD, and come down: touch the mountains, and they shall smoke.
Bow thy heavens, O Lord, and come down - from Psalms 18:9: cf. Isaiah 64:1; borrowed from the same source. What Yahweh has shown Himself toward David during his persecution by Saul, be now prays Him to prove Himself again to him, to his seed, and to Israel.
Touch the mountains, and they shall smoke. "The mountains" symbolize God-opposed world-kingdoms, which at the mere touch of God smoke: the token of fear and the prelude of being consumed by the coming fire of His wrath (Psalms 104:32, note).