Genesis 39:5 From the time that he made him overseer in his house and over all that he had, the Lord blessed the Egyptian's house for Joseph's sake; the blessing of the Lord was on all that he had, in house and field.

In this verse Joseph has been purchased and enslaved by an Egyptian and is so beloved by God that, for the sake of Joseph, he blesses the house of Joseph's owner. Why wouldn't God use this opportunity to do something about the practice of slavery? Joseph's owner only seems to benefit from his purchase and ownership of Joseph. Does God support slavery? Why, when choosing to intervene, does he decide that blessing the house of a slave-owner is the best way to demonstrate his love for Joseph? Is it ever made clear why it was necessary for God to let Joseph remain enslaved?