en_tn_condensed/isa/60/20.md

for Yahweh will be your everlasting light

Both verses repeat this same idea for emphasis. (See: rc://en/ta/man/jit/figs-parallelism)

Your sun will no longer set, nor will your moon withdraw and disappear

The moon will not literally disappear. This exaggeration is saying that the light of the sun and the moon will be much less bright than the light of Yahweh. (See: rc://en/ta/man/jit/figs-metaphor and rc://en/ta/man/jit/figs-hyperbole)