How did Joseph know?

Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law. 15 They show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts sometimes accusing them and at other times even defending them.) Romans 2:15-15 (NIV)

I think this would not be a huge stretch to apply this back to Joseph. If the law is in the hearts and consciences of gentiles, how much more would it have been in Joseph.

Couple of things -

I assume that even before the Law was given to Moses, Abraham and family still had some ideas of God and what was okay with God. God did call Abraham to leave his home, promised him a son, ect. So those beliefs and values would have then been transmitted to his son, and ect. down to Joseph. I mean, it's not like the Ten Commandments just leaped out of nowhere, with no prior knowledge of God of cultural reference points. Joseph was old enough when he was sold into slavery to have retained his early childhood education.

Adultery and the wrongness of it is very nearly a cultural universal - meaning that almost all cultures, even ones cut off from contact with all other civilizations, would consider it bad. This would have included Egypt, and Joseph had been in Egypt long enough to understand their laws and practices to some extent, one would think.

There was no need for him to have had some kind of prophetic or supernatural knowledge imparted to him that oath breaking and defiling another man's wife was not OK with God.

ByTheSpirit said:

This was several hundred years before the Law or any scripture came, so how did Joseph know God was not okay with the proposed action?

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God has given us all a conscience. There are things that in every culture, language and tribe, even people living in rainforests, are seen as so abhorrent that you don't need to be told that it is wrong. Something in a person recoils at them.

This is one. In this example it would not just be the adultery, but the abuse of trust. Potiphar trusted Joseph. It's basic morality not to abuse someone's trust.

Also I think Abraham, Isaac and Jacob, having met with God, something of God's standards and holiness would have rubbed off on them and been passed down.

Maybe God just sort of tugged on the heart of Joseph, he also spoke before the Bible was written.

ByTheSpirit said:

Genesis 39:9 ESV

He is not greater in this house than I am, nor has he kept back anything from me except you, because you are his wife. How then can I do this great wickedness and sin against God?”

Joseph when he was tempted by Potiphar's wife told her it would be a sin against God to submit to her demand. This was several hundred years before the Law or any scripture came, so how did Joseph know God was not okay with the proposed action?

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Even that king knew that it was a sin, but he didn't know Sarah was Abraham's wife. I guess Abraham told his son etc, but that that started with Noah.
They saw nothing wrong in more wives and slaves as wives though. Wasn't forbidden later either.

ByTheSpirit said:

Genesis 39:9 ESV

He is not greater in this house than I am, nor has he kept back anything from me except you, because you are his wife. How then can I do this great wickedness and sin against God?”

Joseph when he was tempted by Potiphar's wife told her it would be a sin against God to submit to her demand. This was several hundred years before the Law or any scripture came, so how did Joseph know God was not okay with the proposed action?

Click to expand...

as a child..you knew when you were first wronged and how it was "not fair" no one needed to explain to you that you were wronged by another...
Joseph learned what it felt like to be wronged as a young lad on a sunny day in his dads joyful coat... stripped cast aside and betrayed into slavery ,torn from family and home mother and father...he learned Acutely how it felt...
he did not desire to wrong his master...

sometimes you just know what God thinks about things.

ByTheSpirit said:

Genesis 39:9 ESV

He is not greater in this house than I am, nor has he kept back anything from me except you, because you are his wife. How then can I do this great wickedness and sin against God?”

Joseph when he was tempted by Potiphar's wife told her it would be a sin against God to submit to her demand. This was several hundred years before the Law or any scripture came, so how did Joseph know God was not okay with the proposed action?

Click to expand...

even then , the spirit bears witness. but just as important, adam and chavah knew, and taught all their children, and their grand children, and parents taught their children, as Yhvh had taught them. abraham, faithful, and faithfully, taught his children (though yes they did make mistakes, but yhvh intended it for good, though they thought otherwise until the truth was finally disclosed).

joseph may have been taught in his sleep and in dreams, as well, as it is also thus written in psalms and/or elsewhere.