What does Genesis 30:4 mean?

Rachel, desperate for children and unable to have any of her own, has given to Jacob her servant girl Bilhah. Any children they have together will belong to Rachel by proxy. Jacob apparently agrees to this plan; we're told of no objections from him. He takes Bilhah as his wife and begins to have relations with her. This is very similar to how Rachel's grandmother, Sarah attempted to have a child, through her servant Hagar, after being unable to conceive with Abraham (Genesis 16:1–4).

To modern readers, the circumstances out of which Jacob's children are born seem far less than ideal. Leah is unloved by her husband (Genesis 29:31. Rachel appears unwilling to trust God and wait on Him (Genesis 30:1–3). Bilhah is, in essence, a slave-wife (Genesis 29:29). In fact, the situation is tragic, and only becomes more dysfunctional over time, as the two sisters engage in a "birth race," competing to produce more sons. Still, God will keep His promises to Abraham and Jacob through these wives and children. As He does even today, the Lord will accomplish His purposes, even through sinful and conflicted people.