Commentary for Genesis 16:2

אולי אבנה ממנה IT MAY BE THAT I SHALL BE BUILDED UP THROUGH HER — This statement of Sarah teaches that a person who has no children is not firmly established (literally, built up: his name and future are not perpetuated) but is unstable (lit, demolished) (Genesis Rabbah 45:2).

AND ABRAM HEARKENED TO THE VOICE OF SARAI. Scripture does not state, “And he did so.” Rather it says that he hearkened to the voice of Sarai, thus indicating that even though Abram was very desirous of having children, he did not do so without permission of Sarai. Even now it was not his intention to build up a family from Hagar, and that his children be from her. His intent was merely to do Sarai’s will so that she may build a family from Hagar for she will find satisfaction in her handmaid’s children, or that by the merit of this act she will become worthy to have children, as our Rabbis have said.³⁵¹Bereshith Rabbah 71:7.
Scripture further says, And Sarai took,³⁵²Verse 3 here. to inform us that Abram did not hurry the matter until Sarai took Hagar and gave her to him. Again, Scripture mentions Sarai Abram’s wife… to Abram her husband,³⁵²Verse 3 here. to allude that Sarah did not despair of Abraham and that she did not render herself distant from him as she was his wife and he her husband, but she wanted that Hagar also be his wife. This is why the verse states, And she gave her to Abram her husband to be his wife,³⁵²Verse 3 here. meaning that she was not to be as a concubine but as a woman married to him. All this reflects the ethical conduct of Sarah and her respect towards her husband.

הנה עצרני ה' מלדת, "even though G'd has promised to grant you offspring to whom I will give this land, (Genesis 12,7) He has not said that the mother of Avram's offspring would be I."