To harden one's own heart/ (to harden someone's heart/ make him stubborn)
He revealed hardness and tightness. He became cruel.
("Blessed is the man who fears continually, but he who hardens his heart will fall into evil" - Proverbs of the Strength of Hand)
Translation
Expression (Hebrew)
הִקְשָׁה אֶת לִיבּוֹ (הִקְשָׁה אֶת לִיבּוֹ שֶׁל...)
Definition (Hebrew)
גִּלָּה קְשִׁיחוּת וַאֲטִימוּת. הִתְאַכְזֵר.
("אַשְׁרֵי אָדָם מְפַחֵד תָּמִיד וּמַקְשֶׁה לִבּוֹ יִפּוֹל בְּרָעָה"- מִשְׁלֵי כֹּחַ יָד)