Genesis 29:28

Verse Genesis 29:28. And Jacob did so - and he gave him Rachel] It is perfectly plain that Jacob did not serve seven years more before he got Rachel to wife; but having spent a week with Leah, and in keeping the marriage feast, he then got Rachel, and served afterwards seven years for her. Connections of this kind are now called incestuous; but it appears they were allowable in those ancient times. In taking both sisters, it does not appear that any blame attached to Jacob, though in consequence of it he was vexed by their jealousies. It was probably because of this that the law was made, Thou shalt not take a wife to her sister, to vex her, besides the other in her life-time. After this, all such marriages were strictly forbidden.