Here "David" represents all the descendants of David. Alternate translation: "a descendant of David to be their king" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Here "trembling" represents feelings of awe and humility. Alternate translation: "they will come back to Yahweh and will humble themselves, honor him, and ask for his blessings" (See: [[rc://en/ta/man/translate/figs-metonymy]])