What does Genesis 16:4 mean?

Now Sarai, Abram’s wife, bore him no children. She had a servant, an Egyptian, whose name was Hagar.

Sarai said to Abram, “See now, Yahweh has restrained me from bearing. Please go in to my servant. It may be that I will obtain children by her.” Abram listened to the voice of Sarai.

Sarai, Abram’s wife, took Hagar the Egyptian, her servant, after Abram had lived ten years in the land of Canaan, and gave her to Abram her husband to be his wife.

Sarai said to Abram, “This wrong is your fault. I gave my servant into your bosom, and when she saw that she had conceived, I was despised in her eyes. Yahweh judge between me and you.”

But Abram said to Sarai, “Behold, your maid is in your hand. Do to her whatever is good in your eyes.” Sarai dealt harshly with her, and she fled from her face.

Yahweh’s angel found her by a fountain of water in the wilderness, by the fountain on the way to Shur.