en_obs-tn/content/05/01.md

still did not have a child

Without a child, Abram had no descendants to become a great nation.

Marry her also

Abram would take Hagar as a second wife, but Hagar would not have the full status of a wife as Sarai did. She was still Sarai's servant.

have a child for me

Since Hagar was Sarai's servant, Sarai would be considered the mother of any children that Hagar bore.