en_tn_condensed/jer/46/27.md

my servant Jacob, do not fear. Do not be dismayed, Israel

These two phrases mean the same thing and are combined for emphasis. Both "Jacob" and "Israel" here represent the nation of Israel.(See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-parallelism)

this is Yahweh's declaration

See how you translated this in Jeremiah 1:7.

will certainly not leave you unpunished

"will certainly punish you." (See: rc://en/ta/man/translate/figs-litotes)