Then the earth shook and trembled; the foundations also of the hills moved and were shaken, because he was angry.
Read Chapter 18
Augustine of Hippo
8. "And the earth was moved and trembled" (ver. 7). When the Son of Man was thus glorified, sinners were moved and trembled. "And the foundations of the mountains were troubled." And the hopes of the proud, which were in this life, were troubled. "And were moved, for God was wroth with them." That is, that the hope of temporal goods might have now no more establishment in the hearts of men. ...
With them is not in Hebrew. Lo, illi refers to God. Furor fuit ei. (Montanus)
"He was wroth. "(Protestants) Yet he displayed his power on the mountains, as if he had been displeased with them, or with the enemies (ver. 4.) whom he would thus strike with awe. (Haydock)
These expressions are not to be taken in a gross literal sense. (Calmet)
God showed himself as earnest in the protection of David, (Haydock) as if he had been in a rage; (Calmet) or as if the elements had all conspired to defend him. (Theodoret)
This most pompous description (Calmet) alludes to the wonders wrought at Sinai, and the terrors which would happen at the death and resurrection of Christ, and at his last coming. Some moderns think that the overthrow of the Babylonians, and other enemies of God's people, are also denoted. The sinner, touched by divine grace, implores mercy, and feels the remorse of conscience, the ropes or sorrows of hell, and a dread of God's just judgments hanging over him. (Berthier)