창세기 30:9의 주석

WHEN LEAH SAW THAT SHE HAD LEFT OFF BEARING SHE TOOK ZILPAH HER HANDMAID, etc. I do not know what motivated this deed of Leah and why she gave her handmaid to her husband for she was not barren that she should hope to have children through Zilpah, and it is not natural for women to increase the number of their husbands’ wives. We must, however, say that the matriarchs were prophetesses,¹⁰⁸Bereshith Rabbah, end of Chapter 72. who knew that Jacob was destined to establish twelve tribes, and Leah desired that the majority of his sons be from her or from her handmaid, who was in her power, so that her sister Rachel would not prevail over her with respect to the number of her sons. Therefore, she said, G-d hath given me my share, because I have given my handmaid to my husband.¹⁰⁹Verse 18 here. Jacob also came unto her on account of this, i.e., that he raise many sons for he knew it to be so, as our Rabbis have said.¹¹⁰Bereshith Rabbah 70:17. Jacob was also aware that he was destined to establish twelve tribes.
It is possible that knowing that the Land had been given to their children, and realizing that Abraham and Isaac had not had many children, Jacob wanted to have many wives in order to increase his progeny so as to inherit the Land, for a fourth generation shall come hither again,¹¹¹Above, 15:16. and so Leah wanted to give him her handmaid so that he would not wed a stranger.

ותרא לאה, she thought that she was not going to have any more children herself, and gave her handmaid to Yaakov seeing that the matriarchs’ main concern was to increase the number of children that would be born for Yaakov.

ותרא לאה כי עמדה מלדת, “Leah became aware that she had stopped becoming pregnant, etc.” Nachmanides endeavours to justify Leah giving her servant maid Zilpah to Yaakov as a wife although she was not barren and had already born 4 sons for her husband. He suggests that Leah, as a prophetess, was aware that 12 sons would be born for Yaakov, and she wanted to be sure that the majority would be from her or her family. The reason that Yaakov agreed was that he, too, wanted to have more sons. It is possible that seeing that Yaakov knew that the land of Canaan had been given to Avraham, and both Avraham and Yitzchok had not produced many children, Yaakov wanted to make up for this by marrying a number of women. He knew that the fourth generation of Avraham’s descendants would return to the land of Canaan to take possession of it.