Both phrases mean Yahweh will shout with a loud, clear and powerful voice from Jerusalem. If your language only has one word for speaking very loudly, this can be used as one phrase. Alternate translation: "Yahweh will shout from Jerusalem" (See: [[rc://en/ta/man/translate/figs-parallelism]])
Joel speaks of the heavens and earth as if they were people who are shaking with fear. This can be translated as either a hyperbole, that Yahweh's roar is so frightening that even things that are not alive are afraid, or as metonymy, that the heavens and earth are metonyms for the beings who live there. Alternate translation: "Everyone in the heavens and on the earth is very afraid" (See: [[rc://en/ta/man/translate/figs-hyperbole]] and [[rc://en/ta/man/translate/figs-metonymy]])
Both of these phrases mean Yahweh will protect his people. A fortress is a strong shelter used to protect people during war. Alternate translation: "Yahweh will be a strong fortress for his people, the people of Israel" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-parallelism]])