What does Genesis 31:16 mean?

Rachel and Leah are telling Jacob why they will support him in what will become a quick and secret move away from Laban, and toward Jacob's homeland in Canaan (Genesis 31:3). Both feel their father has mistreated them, in part, by treating Jacob so badly (Genesis 30:31–36). From their perspective, their father more or less sold them to gain free labor from Jacob (Genesis 29:20–28), leaving them no gain, and has continued to cheat their husband, further harming their finances. He might also have been cold or unfriendly to them after their marriage. Neither woman expects to receive any inheritance from Laban when he dies.

Finally, in this verse, they declare they already have their father's wealth, anyway. They repeat what Jacob has already said: God took Laban's wealth and gave it to them. In fact, they say their father's wealth already "belongs to us and our children." In other words, they have no financial incentive not to run away from their father never to return again.

It's interesting to note that Rachel and Leah focus their reply on financial issues. This might be a deliberate slam against Laban—since his interests are purely about money, they can make a good case to leave him, based on money. It might also reveal how little emotional attachment they have to their father or brothers or homeland. They offer no reason not to support Jacob in this move. They conclude by saying he should do whatever God has said to do—a welcome point of unity between sisters who are also bitter rivals (Genesis 30:8).

Did Jacob feel he needed their permission to do what God had told him? It's not clear, but Jacob's wives did give him their support. That was the last piece he was waiting for to take action.