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

These two phrases mean the same thing. Here "Jacob" and "Israel" represent the people of Israel. Yahweh is emphasizing that the people should not be afraid. AT: "people of Israel, my servants, do not be afraid" (See: rc://en/ta/man/translate/figs-parallelism and rc://en/ta/man/translate/figs-metonymy)

from the land of their captivity

"from the land where they are captives"