Sarah Shall Establish My Covenant

God tells Abraham that his covenant goes through Sarah and Isaac, not through Ishmael. The chosen line is specified - it goes through Sarah, the wife Abraham loves, not the servant Hagar.

This is harsh for Hagar and Ishmael, but it's clear. Covenant goes where God chooses, not where human logic or preference suggests.

I struggle with the exclusivity of it - why does the promise have to exclude some people to include others? The text doesn't answer that. It just establishes that covenant has boundaries.