It is not clear as to what the mechanism God uses to harden hearts is; allowing such or in someway forcing such. It would be easy not knowing why God would want such for us to have difficaulty with this passage. With such passages it is best to give God the bennefit of our doubt and seek through for a more understandable why.
Why? Hearts tend to harden or soften on their own given situations whether reasonably our unreasonably. These peoples hearts had been hard and continue to be unreasonably hard to this day. Perhaps God knowing that their hearts would not soften (or only temporarily) set in motion the final hardening (atleast for this time). Neither do we know the demonic warfare occurring behind the scenes that God may have been cleansing out of the area.
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