Genesis 30:3

She shall bear upon my knees - The handmaid was the sole property of the mistress, as has already been remarked in the case of Hagar; and therefore not only all her labor, but even the children borne by her, were the property of the mistress. These female slaves, therefore, bore children vicariously for their mistresses; and this appears to be the import of the term, she shall bear upon my knees.

That I may also have children by her - ואבנה ממנה veibbaneh mimmennah, and I shall be built up by her. Hence בן ben, a son or child, from בנה banah, to build; because, as a house is formed of the stones, etc., that enter into its composition, so is a family by children.

30:3 Behold my maid, Bilhah - At the persuasion of Rachel he took Bilhah her handmaid to wife, that, according to the usage of those times, his children by her might be adopted and owned as her mistresses children. She would rather have children by reputation than none at all; children that she might call her own, though they were not so. And as an early instance of her dominion over the children born in her apartment, she takes a pleasure in giving them names, that carry in them nothing but marks of emulation with her sister. As if she had overcome her, At law, she calls the flrst son of her handmaid, Dan, Judgment, saying, God hath Judged me - That is, given sentence in my favour. In battle, she calls the next Naphtali, Wrestlings, saying, I have wrestled with my sister, and have prevailed - See what roots of bitterness envy and strife are, and what mischief they make among relations!