What does Genesis 39:9 mean?
Joseph is explaining to his master's wife (Genesis 39:1) that he will not go to bed with her, as she has demanded (Genesis 39:7). His reasons are not about personal risk, or personal danger, but the fact that such a betrayal would be dishonorable. Potiphar has put enormous trust in Joseph. Potiphar trusts Joseph so much that he doesn't even check to see how Joseph is managing all the needs of his large estate. He knows Joseph will do everything with excellence (Genesis 39:4–6).In fact, Potiphar has given Joseph equal authority as himself in his own household. Because Potiphar trusts him, Joseph can literally do whatever he likes, whatever is required. The one thing Potiphar has made off-limits to Joseph is his wife—likely not a restriction that needed to be said. If it was mentioned, directly, it might suggest that Potiphar knew his wife was unfaithful.
Given the trust with which he's been gifted, Joseph realizes such a sin would be especially heinous. His motive for good behavior is not fear or self-interest, but a sincere conscience. Joseph seeks to live up to the trust and honor placed in him by both Potiphar and the Lord.