TSK · Genesis 16:1

But Sarai was barren; she had no children.

But Abram said,“O Sovereign LORD, what will you give me since I continue to be childless, and my heir is Eliezer of Damascus?”

But God said to Abraham,“Do not be upset about the boy or your slave wife. Do all that Sarah is telling you because through Isaac your descendants will be counted.

Isaac prayed to the LORD on behalf of his wife because she was childless. The LORD answered his prayer, and his wife Rebekah became pregnant.

But they did not have a child, because Elizabeth was barren, and they were both very old.

These things may be treated as an allegory, for these women represent two covenants. One is from Mount Sinai bearing children for slavery; this is Hagar.