People expect mountains and hills to be stable. Yahweh speaks of the possiblity of them falling and being shaken to show that his steadfast love and his covenant of peace are even more stable. Alternate translation: "Even if the mountains were to fall and the hills were to shake, my steadfast love will not ... be shaken"
Yahweh's continuing to love his people is spoken of as if his love would not turn away from the people. Alternate translation: "I will not stop loving you" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Yahweh's not canceling his covenant with the people is spoken of as if his covenant were an object that would not be shaken. This can be stated in active form. Alternate translation: "and I will not cancel my covenant of peace" or "and I will surely give you peace as I promised in my covenant" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-activepassive]])
Here Yahweh speaks about himself in the third person. It can be stated in first person. Alternate translation: "that is what I, Yahweh, who acts mercifully, say" (See: [[rc://en/ta/man/translate/figs-123person]])