en_tn_condensed/isa/55/11.md

so also my word ... it will achieve the purpose for which I sent it

Yahweh speaks of his word as if it were a person whom he sends out as his messenger to accomplish a task. (See: rc://en/ta/man/translate/figs-personification and rc://en/ta/man/translate/figs-metaphor)

my word will be that goes from my mouth

Here the word "mouth" represents Yahweh himself. Alternate translation: "the word that I speak" (See: rc://en/ta/man/translate/figs-synecdoche)

it will not return to me empty

Here the description of the word returning to Yahweh means that it has completed the task that Yahweh had sent it to complete. That it will not return "empty" means that it will not fail to accomplish its task. Alternate translation: "it will not fail to complete its task" (See: rc://en/ta/man/translate/figs-explicit)