As Pharaoh had wittingly hardened his heart with each of the first five plagues, and refused to turn from his sinful purpose, God punished him thereafter in such wise that he could not mend his ways if he would. God said, "Even though he should desire to do penance now, I will harden his heart until he pays off the whole of his debt."
Pharaoh had observed that whenever he walked on the brink of the Nile, Moses would intercept him. He therefore gave up his morning walk. But God bade Moses seek the king in his palace in the early hours of the day and urge him to repent of his evil ways. Therefore Moses spake to him as follows, in the name of God: "O thou villain! Thou thinkest that I cannot destroy thee from the world. Consider, if I had desired it, instead of smiting the cattle, I might have smitten thee and thy people with the pestilence, and thou wouldst have been cut off from the earth. I inflicted the plague only in such degree as was necessary to show thee My power, and that My Name may be declared throughout all the earth. But thou dost not leave off treading My people underfoot. Behold, to-morrow when the sun passes this point,"--whereat Moses made a stroke upon the wall--"I will cause a very grievous hail to pour down, such as will be only once more, when I annihilate Gog with hail, fire, and brimstone."