Here's an interesting take related in the Jerusalem Post:
"Rashi notes that the process of increasing punishments was necessary to demonstrate God’s power – not only to the Egyptians, but to the Jews. He notes that during the first five plagues, Pharaoh himself was responsible for his hardening heart.
In addition, Pharaoh’s heart was “strengthened.” (Exodus 7:13) and then became “heavy.” (Exodus 7:14) Why does the Torah use three different words to describe what amounts to a single description of his stubborn obstinacy? We will answer this shortly.
Rambam, Rabbi Moshe ben Maimon, (Mishne Torah, Hilchot Teshuva) insists that everyone has free will; one can choose to do good, or evil. The ability to choose freely defines us as human beings; our choices define us as individuals. Freedom to choose is an essential and inherent right, but it is not absolute; there are consequences to actions.
This explains why three different words are used to describe Pharaoh’s heart. He changes his mind, perhaps from lack of awareness and fear of losing a valuable commodity. It’s understandable, given his position. That is what is meant by “hardening,” and “heavy.” He refuses to change, even though he recognizes God’s existence. But then he becomes recalcitrant and arrogant – which is described as “his heart was strengthened.”
The key to understanding this psychological debilitation – and what Torah teaches – is Pharaoh’s lack of self-criticism. The ability to choose, to exercise free will without honest self-evaluation and introspection, is self-destructive and destructive to others. In Pharaoh’s case, he led his army and his nation to disaster."
My thoughts: Perhaps after 5 times that Pharaoh changed his mind, God finally gave him the complete separation from common sense he sought so Pharoah could completely indulge his self-centeredness? If so, this allowed for greater displays of protection for the Israelites that should have formed a larger basis of trust for them.
The God of the ot is not morally acceptable by any standard
Well, I think that billions of people would disagree with that statement. It is the basis of our judicial courts and all of judeo-christian western culture.... the greatest and freest culture ever seen on earth.