Genesis 29:20

And Jacob served seven years for Rachel; and they seemed unto him but a few days, for the love he had to her.

Jacob served Laban seven years to gain Rachel as his wife, his labor itself being the agreed payment for the marriage. Having no money or other valuable property to offer, he paid the bride-price by working for Rachel's father, with the required period of work fixed according to the value of the dowry demanded. Where a suitor possessed no money or goods, he could thus satisfy the claim by labor for a set time determined by that required dowry.

That custom of labor for a bride also furnished time to test the suitor, proving both his worthiness and the depth of his affection before the marriage took place. Jacob's love for Rachel made those seven years of willing, faithful labor seem to him but a few days, brief and light, and his affection sustained him through the long toil he undertook for her. His years of service for her felt for that reason like a light toil. When the service was completed, Laban deceived him by giving him Leah as wife instead of Rachel.