וַיַּ֤רְא יְהוָה֙ כִּֽי־שְׂנוּאָ֣ה לֵאָ֔ה וַיִּפְתַּ֖ח אֶת־רַחְמָ֑הּ וְרָחֵ֖ל עֲקָרָֽה׃
And the LORD saw that Leah was hated, and he opened her womb; but Rachel was barren.
Read kabbalistic (mystical) interpretation of Genesis 29:31: and classical mystical sources.