Why is it said that God hardened Pharaoh's heart? Surely God would not cause sin.
You're right! God hates sin. More than we can imagine. He wouldn't do anything to bring it about.
The Old Testament isn't as nuanced in its language as we would generally expect. In more precise terms, we might prefer to say that God gave Pharaoh his freedom, and that Pharaoh used it poorly, so much so that his heart was hardened.
But the Old Testament authors tended to compress all of that into a single statement: "God hardened Pharaoh's heart." Not very nuanced, right? It is however correct in this sense: God is the one ultimately "responsible" because he chose to make Pharaoh free, even though we would put the accent on Pharaoh's sin.
It's a pattern that we see all through the Old Testament: It sounds like God is being blamed for something lousy, whereas it's really just correctly saying that God is the maker and origin of all things.
So let's just focus on what God tells all of us in Psalm 95: "If today you hear his voice, harden not your hearts!" Anyway, that's my understanding of it, certainly not as a Biblical scholar.
God bless you!
- Father Shane