Isaiah introduces this desire for Yahweh's presence in their past history with a strong exclamation. (See: [[rc://en/ta/man/translate/figs-hypo]])
# if you had split open the heavens
If Yahweh had shown himself very dramatically by tearing open the sky. The words "split open" refer to ripping a piece of cloth apart. (See: [[rc://en/ta/man/translate/figs-metaphor]])
# mountains would have shaken
The mountains would have trembled as in an earthquake. (See: [[rc://en/ta/man/translate/figs-hypo]])
# as when fire kindles the brushwood, or the fire makes water boil
This possibly emphasizes how easily God's presence would have caused the mountains and the people to tremble. (See: [[rc://en/ta/man/translate/figs-simile]] and [[rc://en/ta/man/translate/figs-hypo]])