"But is it not said that God hardened Pharaoh's heart? Here is more than barely permitting sin.
God does not infuse evil into men, he
withdraws the influence of his graces, and then the heart hardens of
itself; even as
the light being withdrawn, darkness presently follows in the air;
but it were absurd to say, that therefore the light darkens
the air; and therefore you will observe, that Pharaoh is said to
harden his own heart. Exod 8:15.
God is the cause of no man's sin. It is true God has a hand in the
action where sin is, but no hand in the
sin of the action. A man may play upon a jarring instrument, but
the jarring is from itself; so here, the actions of men,
so far as they are natural, are from God; but so far as they are
sinful, they are from men themselves, and God has no hand
at all in them." (Thomas Watson, A Body of Divinity)
Psalm 105:25, Romans 9:18, and the relevant passages in Exodus blatantly contradict Watson's erroneous assertion that God does not cause man's sin.