Genesis 39:21

“And the Lord was with Joseph, etc.] Comforting him with his presence under his afflictions; supporting him with his right hand; sanctifying all his troubles to him, and so causing him to bear them patiently and cheerfully: and showed him mercy, and gave him favour in the sight of the keeper of the prison; who was the underkeeper to Potiphar; God so wrought upon the heart of this man, that he was merciful to him, and took off the iron fetters, which hurt his feet, and gave him liberty to walk about; and many other favours and kindnesses he showed unto him, as follow.”

“The Lord . . . gave him favour in the sight of the keeper of the prison, &c.--It is highly probable, from the situation of this prison (Gen 40:3), that the keeper might have been previously acquainted with Joseph and have had access to know his innocence of the crime laid to his charge, as well as with all the high integrity of his character. That may partly account for his showing so much kindness and confidence to his prisoner. But there was a higher influence at work; for "the Lord was with Joseph, and that which he did, the Lord made it to prosper." Next: Genesis Chapter 40”

“- Joseph in Potiphar’s House According to our reckoning, Perez and Zerah were born when Judah was in his twenty-eighth year, and therefore, Joseph in his twenty-fourth. Here, then, we go back seven years to resume the story of Joseph. Genesis 39:1-6 Joseph fares well with his first master. “Potiphar.” This is a racapitulation of the narrative in Genesis 37:0: “The Lord;” the God of covenant is with Joseph. “In the house.” Joseph was a domestic servant. “And his master saw.” The prosperity that attended all Joseph’s doings was so striking as to show that the Lord was with him. “Set him over” - made him overseer of all that was in his house. “The Lord blessed the Mizrite’s house.” He blesses…”

“39:21-23 Joseph thrived in prison because God was with him. Each time Joseph prospered, he was put in charge of something.”