The 11th of Nisan is the Yahrtzeit of Rav Moshe ben Nachman, the Ramban: This is what the Sages say: One who comes to cleanse himself, they will help him from heaven, that is, God promises you, if you will return to Him with all your heart, He will help you.
From the inception of Creation, it was up to man to choose freely between being righteous or wicked. Particularly with the Giving of the Torah, choosing good brings merit, whereas the choice of bad, entails punishment. But in the era of the Messiah, the choice of good will come naturally; the heart won't lust for something unsuitable and will not want it at all. This is the circumcision of the heart mentioned here.
Because desire and lust are in the heart, and circumcision of the heart means not to desire or lost. During that utopian era, man will return to the state of Adam prior to his sin, when he did it naturally would he was supposed to do, and he did it on something and it's opposite.
This is the meaning of, “Behold, there will come days, says the Lord, when I will make a new covenant with the House of Israel and the House of Judah, unlike the covenant with their fathers (Jeremiah 31:30–31) to see,” for at this new covenant with the House of Israel, following those days after their return from exile, My Torah will be in their midst and be written on their hearts, that is, this is the abolishment of the evil inclination and the hearts pursuing its naturally suitable inclination.