Here "King" refers to Yahweh. This can be stated in first person. Alternate translation: "this is what I, the King, declare" (See: [[rc://en/ta/man/jit/figs-123person]])
This refers to the nation of Babylon who will be as overwhelming to the nation of Egypt as the these two mountains are to the plains that surround them. (See: [[rc://en/ta/man/jit/figs-simile]])