This double negative emphasizes that the lost sheep are the only ones to whom Jesus was sent. Alternate translation: "I was sent only to the lost sheep ... Israel" (See: [[rc://en/ta/man/jit/figs-doublenegatives]])
This is a metaphor comparing the entire nation of Israel to sheep who have gone away from their shepherd. See how you translated this in [Matthew 10:6](../10/06.md). (See: [[rc://en/ta/man/jit/figs-metaphor]])