To make up one's mind/ decide/ come to a conclusion

He decided in his heart. He came to a conclusion between himself and himself.

(“As Samuel said: If one resolves in his heart, he must articulate it with his lips; and this teaches us that even though he did not articulate it with his lips…” — Tractate Chagigah 10a And likewise: “Anyone who confesses verbally but has not resolved in his heart to abandon [the sin] is like one who immerses while holding a creeping thing in his hand—the immersion does not benefit him until he throws away the creeping thing.” — Maimonides, Mishneh Torah, Mishneh Torah, Hilchot Teshuvah, ch. 2, §3 And likewise: “He was truly distressed by the situation… and I resolved in my heart: Whatever may come upon me, I will put an end to the matter!” — Sholem Aleichem, Etsah, no. 109 And likewise: “One wished to study medicine, and another had still not resolved in his heart what he would do.” — S. Y. Agnon, Temol Shilshom, p. 176)

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