What does Genesis 30:15 mean?Rachel has requested some of the mandrake plants Leah's son has found (Genesis 30:14). Mandrake plants, apparently, were thought to have aphrodisiac qualities and to be an aid to infertility. These two infertile sisters were likely interested in the plants for exactly that reason. Leah was able to bear four sons for Jacob, but has now stopped conceiving (Genesis 29:31–35). Rachel has never been able to have a child through her own womb. Both have obtained children through their servants, as part of a competition between these sisters (Genesis 30:1–13). Any item believed to aid in conception would have been precious to both women.
Leah responds to Rachel's seemingly-polite request with surprising anger, and with great emotion. Even after the years that have passed and the sons Leah has given to Jacob, it's clear that this conflict is not resolved. Rachel likely still envies her sister for the children she has birthed, and Leah is definitely burdened by the constant awareness that Jacob still loves Rachel and not her (Genesis 29:31).
Her statement that Rachel has "taken away her husband," in light of what follows, reveals to us that Jacob is likely no longer sleeping with Leah. His desire for Rachel has given her full control over his affection and attention. Leah has been left on her own. It's not surprising that she's not inclined to share her mandrakes, especially if she believes they may help Rachel to become pregnant and cement Jacob's preference for her.
Rachel responds with a revealing offer: Leah can have Jacob for one night. Not only does this show us just how much power Rachel has over Jacob, it also shows us how desperate she is for anything which can help her get pregnant. The offer itself also strongly indicates that Leah's recent lack of fertility is directly due to Rachel's influence over Jacob (Genesis 29:35). Leah's acceptance of this offer, in turn, shows her desperation to become pregnant again, as well as her eagerness to spend more time with Jacob.