וַתֹּ֕אמֶר הִנֵּ֛ה אֲמָתִ֥י בִלְהָ֖ה בֹּ֣א אֵלֶ֑יהָ וְתֵלֵד֙ עַל־בִּרְכַּ֔י וְאִבָּנֶ֥ה גַם־אָנֹכִ֖י מִמֶּֽנָּה׃
האָט זי געזאָגט: אָט איז מײַן דינסט בלהָה, קום צו איר, און זי װעט געבערן אױף מײַנע קני, און אױך איך װעל אױפֿגעריכט װערן פֿון איר.
Rashi
על ברכי UPON MY KNEES — as the Targum takes it: she will bear children and I will rear them.
Radak
ותאמר, she said that after Yaakov had explained to her that her failure to have children was G’d’s doing, she suggested what Sarah had suggested to Avraham, that she was willing to become a vicarious mother through her servant maid having a child by him. She therefore asked Yaakov to sleep with Bilhah.
Sforno
בוא אליה, this was Rachel’s answer to her husband’s accusation. She had not meant that it was within Yaakov’s power to make her pregnant, but she wanted to nurse a child by the next best method, that of becoming foster mother to her handmaid’s child.
Or HaChaim
צוטריטלעך נאָר פֿאַר פּרעמיום־מיטגלידערTur HaArokh
צוטריטלעך נאָר פֿאַר פּרעמיום־מיטגלידערSiftei Chakhamim
צוטריטלעך נאָר פֿאַר פּרעמיום־מיטגלידערRav Hirsch
צוטריטלעך נאָר פֿאַר פּרעמיום־מיטגלידערRashi
ואבנה גם אנכי AND I ALSO MAY HAVE CHILDREN — What force has “also”? She said to him, “Your grandfather, Abraham, had children from Hagar and yet he girded up his loins (actively interceded) for Sarah and she afterwards was blessed with a child”. He replied, “But my grandmother brought an associate wife unto her house”. She retorted, “If that is what prevents me being blessed with children, הנה אמתי BEHOLD MY HANDMAID” etc.