The word overseer in verse 4 means "One who looks after," and literally means, "One who counts." He was an accountant in our own modern lingo. He was one who counted. From the description of what Potiphar gave regarding Joseph in his duties, we can see that he was actually acting as Potiphar's steward. And Joseph, of all the examples in the Bible, is the premier example of a good and faithful steward. He served willingly, though he was a slave; he was successful because God prospered everything that had been put in his care. He was trustworthy. Potiphar did not seem to care up to this point about what Joseph did because he knew that he would follow through wonderfully and produce profit for him.
Joseph in Hebrews means adding, and as a steward, he managed his master's estate and goods, and they added to his wealth. And that is what a steward is supposed to do—take what has been given to him, guard it, maintain it, and enhance it.
In Genesis 39, Moses records that the LORD caused all that Joseph did to prosper in his hands.
That was as a result of Joseph's righteous effort. We see that God made all of Joseph's effort prosper. All of it.
