מוסר אויף יואל 2:13

When sufferings of chastisement come upon a person, he returns to the good. As the sages interpreted the Song of Songs, "Behold, you are beautiful, my beloved, and pleasant" - even when You bring upon me sufferings of chastisement, it is pleasant. Why? Because You return me thus to the good. Human repentance is never complete without suffering. Repentance is improving one's actions and character. It is not fasting and wearing sackcloth and wallowing in the dust and immersing in water while remaining soiled on the inside with sins and evil thoughts. And so said the prophet (Isaiah 58): "Do you call that a fast, A day when the LORD is favorable?" "No, this is the fast I desire: To unlock fetters of wickedness, And untie the cords of the yoke." [...] The intent of the Torah is that one should first cleanse oneself on the inside, casting out from one's heart the impurities of sin, and then return what one has taken unfairly or by violence, and ask forgiveness from one's friend. After immersing one's heart inwardly and doing all kinds of purification and cleansing oneself from sin, one should purify oneself also outwardly by fasting and immersing the body, and so on...

And since it has become clear that the heart corresponds to the Holy of Holies; such that the Torah and the commandments should rest there (in the heart) corresponding to the tablets - it also appears that one should rend his heart, as it is written (Joel 2:12), "rend your hearts, etc." So his heart will be [such that], "God, You will not despise a broken and crushed heart" (Psalms 51:19). And it is like the broken tablets that were resting in the ark (Bava Batra 14b). So his heart should be broken about an incorrect act or attribute of his, or wasting time from Torah study and that which is similar to it. And he should be greatly distressed, regret it with great regret and make a solid commitment in his heart not to go on this path ever again.

Finally, he should know how to strengthen himself exceedingly and to bear the great burden of restraining himself from that evil which he is accustomed to do. For this is obvious that a sin that he has been accustomed to do all his life he will regard as permissible (Yoma 86b), and it is very difficult for him to give it up. Therefore, a man needs great will power and high fences to give up what he has been accustomed to. And it requires a great accord in all his heart and soul to hold himself back from committing that sin, and he must remove this habit from his heart as though he had not been accustomed to do this. And he must become accustomed to reject in his heart all the evil things, as it is said, "And rend your heart and not your garments" (Joel 2:13). And when the sinner establishes these seven considerations firmly in his heart, he is very near to the path of repentance.