Sefat Emet, Exodus, Bo 8:3שפת אמת, שמות, בא ח׳:ג׳
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Exodus 10:1שמות י׳:א׳
Then יהוה said to Moses, “Go to Pharaoh. For I have hardened his heart and the hearts of his courtiers, in order that I may display these My signs among them,
Exodus 10:2שמות י׳:ב׳
and that you may recount in the hearing of your child and of your child’s child how I made a mockery of the Egyptians and how I displayed My signs among them—in order that you may know that I am יהוה.”
Pirkei Avot 5:1משנה אבות ה׳:א׳
With ten utterances the world was created. And what does this teach, for surely it could have been created with one utterance? But this was so in order to punish the wicked who destroy the world that was created with ten utterances, And to give a good reward to the righteous who maintain the world that was created with ten utterances.
Mesillat Yesharim 2:10מסילת ישרים ב׳:י׳
This is similar to the wicked Pharaoh's advice saying "intensify the men's labor..." (Ex. 5:9). His intention was to leave them no time whatsoever to oppose him or plot against him. He strove to confound their hearts of all reflection by means of the constant, incessant labor.