Musar su Deuteronomio 13:18

“Do not harden your heart and shut your hand” (Deuteronomy 15:7). We were warned with this to remove the trait of cruelty from our souls, and to plant delightful saplings in it - [namely] reliable mercy and kindnesses, as it is written (Deuteronomy 28:9), “and you shall walk in His ways.” And because it is possible not to shut his hand and to grace the poor person, but not in the way of mercy - like the matter that is written (Proverbs 12:10), “but the mercies of the wicked are cruelty” - therefore it is written, “Do not harden your heart.” And the punishment for cruelty is bad and bitter, as will be explained in the Gate of Cruelty (no longer extant), with God’s help. And our Rabbis, may their memory be blessed, said (Shabbat 151b), “‘And He will show you mercy and have compassion on you and multiply you’ (Deuteronomy 13:18) - anyone who has compassion for the creatures will receive compassion from Heaven, and anyone who does not have compassion for the creatures will not receive compassion from Heaven.”

The quality of mercy identifies the descendants of Abraham our father — the seed of Israel as it is written in Deuteronomy 13:18: "And He shall show you mercy and have mercy upon you and multiply you" i.e. (God will give you the quality of mercy). Therefore, everyone should accustom himself to speak all his words with the language of petition and mercy. Also, when he prays, his prayer should be in the tone of plea and petition. And great indeed is the reward that a man will receive from his words of mercy when he speaks to the heart of the poor.

And you, son of man, examine yourself and be far from cruelty and have mercy upon the poor and the needy and let the poor be as the members of your family. "Then the Lord … will show you mercy and have compassion upon you and multiply you" (Deut. 13:18). Everyone who has mercy on his fellow creatures will have mercy shown him from heaven (Shabbath 151b). Therefore, do not remove mercy from you but guard yourself against the quality of cruelty. And Solomon said: "Lest you give to others your vigour and your years unto the cruel (to being cruel)" (Prov. 5:9). And guard yourself against the desire for vengeance which itself stems from cruelty. If you wish to truly avenge yourself on your enemy then add to your good qualities and walk in the path of the upright, and in this way you will be avenged on him who hates you, for he will writhe in pain because of your good qualities and good repute and mourn when he hears good of you. But if you do ugly deeds then your enemy will rejoice over your shame and disgrace and thus avenge himself against you.