Why were Hagar and Ishmael sent away in Genesis 21?
Hagar and Ishmael were sent away because Ishmael had reached the age of tormenting young Isaac, and God instructed Abraham to heed Sarah’s voice. God declared that His promised seed would be called through Isaac, not through the bondwoman’s son.
Les explains that in Genesis 21 Ishmael had reached the age of tormenting little Isaac, who was probably five. Therefore Ishmael and Hagar are sent out at God’s instruction. God tells Abraham not to be grieved over the lad or the bondwoman and to hearken to Sarah’s voice, because in Isaac shall Abraham’s seed be called. Les emphasizes that the Hebrew word for seed, Zerah, can be singular or collective, and here the context points to the singular seed, Christ, rather than the many offspring of Israel.