Why did Hagar despise Sarai after she became pregnant?
Hagar despised Sarai because, having conceived a child by Abram while Sarai remained barren, she exalted herself over her mistress. Sarai said, "When she saw that she had conceived, I was despised." Hagar was making a fool out of Sarai simply because she could bear a child and Sarai could not.
Les explains that Sarai gave Hagar to Abram according to the custom of the day, reflected in the laws of Hammurabi, so that a child could be had through a servant. But they did it in the energy of the flesh, and once Hagar was with child, trouble arose. Sarai complained to Abram, "My wrong be upon thee. I have given my maid into thy bosom, and when she saw that she had conceived, I was despised." Les teaches that Hagar was literally making a fool out of Sarai, her mistress, simply because she was able to bear a child and Sarai was not. This infuriated Sarai, who called on the Lord to judge. Abram told Sarai the maid was in her hand, to do as pleased her, and Sarai then kicked Hagar out.
And he went in unto Hagar, and she conceived: and when she saw that she had conceived, her mistress was despised in her eyes.
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