Yahweh speaks of suffering and difficult experiences as if they are deep waters and fires through which the people walk. The words "waters" and "flames" form a merism and emphasize any difficult circumstance. (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-merism]])
These two statements mean basically the same thing and emphasize that the people will experience no harm because Yahweh is with them. (See: [[rc://en/ta/man/jit/figs-parallelism]])