רמב"ן — ומל ה' אלהיך את לבבך ואת לבב זרעך

Q — What does it actually MEAN that Hashem will "circumcise our hearts" in the future? And how does this square with bechira chofshit, which Chazal insist is the foundation of שכר ועונש?

A — Ramban: the ערלה of the heart is desire itself — "החמדה והתאוה ערלה ללב." In ימות המשיח, after Israel's full teshuva, Hashem will REMOVE desire, so that choosing-good becomes Israel's NATURE — like the heavens and their hosts, "פועלי אמת שפעולתם אמת ולא ישנו את תפקידם." This is a return to אדם הראשון's pre-sin state: before eating from the עץ, Adam acted by nature with no contrary will. The eating of the eitz birthed bechira (= "דעת" = רצון) — a "מדה אלהית" but also a source of יצר and תאוה. Crucial caveat: this divine help comes only AFTER human teshuva — "הבא ליטהר מסייעין אותו" — never as a substitute for the work. And it brings an inevitable consequence: per Chazal on קהלת, ימות המשיח have "לא זכות ולא חובה" — both presuppose bechira, which itself will be transcended.