It is, of course, true that good men are made better both by the forbearance and the severity of God; yet when we speak of good and bad men together, these tropes will turn the mercy of God into wrath and his wrath into mercy by a thoroughly perverse use of language, calling it wrath when God confers benefits, and mercy when he imposes afflictions. But if God is to be said to harden when he confers benefits and exercises tolerance, and to have mercy when he afflicts and punishes, how can he be said to have hardened Pharaoh any more than the Children of Israel or even the whole world? Does he not tolerate the wicked? Does he not send rain on the good and the evil [Matt. 5:45]? Why is he said to have had mercy on the Children of Israel rather than on Pharaoh? Did he not afflict the Children of Israel in Egypt and the wilderness? Granted that some abuse while others rightly use the goodness and the wrath of God; your definition nevertheless equates hardening with showing indulgence to the wicked through forbearance and kindness, whereas showing mercy is the same as not indulging but visiting and punishing. As far as God is concerned, therefore, he does nothing but harden by continual goodness and nothing but show mercy by continual punishment.
The Bondage of the Will
Luther’s Works Vol. 33