St. Maximus on the hardening of Pharaoh’s heart.

12. God, it is said, is the Sun of Righteousness (cf. Mal. 4:2), and the rays of His supernal goodness shine down on all men alike. The soul is wax if it cleaves to God, but clay if it cleaves to matter. Which it does depends on its own will and purpose. Clay hardens in the sun, while wax grows soft. Similarly, every soul that, despite God’s admonitions, deliberately cleaves to the material world, hardens like clay and drives itself to destruction, just as Pharaoh did (cf. Exod. 7: 13). But every soul that cleaves to God is softened like wax and, receiving the impress and stamp of divine realities, it becomes ‘in spirit the dwelling-place of God’ (Eph. 2: 22).

The Philokalia, pg. 116

I, being the good non-Calvinist that I am, have always argued for the distinction between the active and passive Divine wills. The active will of God is the will in which God’s decree sufficiently determines an event. The passive will of God is the will of His in which is necessary for an event to occur, but not sufficient. With this distinction in mind I have asserted that in the case of the hardening of Pharaoh’s heart, this was brought about passively by God and actively by Pharaoh. Thinking thus led met to say things like “It was Pharaoh who hardened his own heart”, and this despite the fact that the verb is predicated on God, not Pharaoh, in Romans 8.
But now I have been enlightened by St. Maximus the Confessor in the passage quoted above, I can affirm the self-same proposition the Calvinist affirms, but without having to concede all the baggage that comes with Calvinism. When I assert “God hardened Pharaoh’s heart”, I mean this in the sense that God’s holiness is such that when it comes into contact with a soul which “cleaves to matter” (i.e. a soul that sins), such a soul hardens as clay hardens in the sun. But acknowledging this truth does not entail that it the case that God made Pharaoh’s heart such that it would be hardened if it came into contact with the Divine. To read it that way would be reading into the text.

Praise be to God for the post-Nicene Patristics!