Genesis 29:23

And it came to pass in the evening, that he took Leah his daughter, and brought her to him; and he went in unto her.

In the evening Laban brought Leah to Jacob instead of Rachel, whom Jacob loved and expected to marry after serving seven years for her, and by that substitution deceived him into marrying Leah. It was customary for a suitor to pay the bride's father a dowry, or if he lacked money or property to work for a stated period, and Jacob's labor was the required payment for his wife. That dowry custom was meant to safeguard the marriage institution, to test the suitor's fitness and the strength of his affection, and to provide for the daughter, since the dowry was generally given to her at marriage. Laban afterward kept for himself the dowry that should have gone to Leah and Rachel.

Leah herself took part in the deception. Jacob reproved Laban for deceiving him. To put Leah away would have been counted a disgrace to her and to her family, so Laban insisted she must remain Jacob's wife. Laban then offered Rachel to Jacob in exchange for another seven years of service, which Jacob served out of his deep love for Rachel.

Jacob kept Leah as his wife and also married Rachel, but he did not love Leah as he loved Rachel, and Rachel remained his favored wife. The rivalry between the sisters embittered Jacob's life.