Musar for Bava Kamma 237:16

He who robs from his companion it is as though he slew him — even if he robs him of a trifle such as only a penny he is deserving of the death penalty. Also this crime belongs under Cruelty — one who spreads slander about his companion and, thus, causes him pain and shame. And he who slanders the morality of a man's family, (such as attacking the legitimacy of his birth) there is no atonement for such a crime to all eternity.

[And his friend will only lose because of this. For it is known that one who robs his friend is only a fool and an evildoer. For his grant will not increase beyond what was decreed for him on Rosh Hashanah, because of his theft. For in exchange for taking the grant that came or that was destined to come to the hand of his friend, there will be taken from him the grant that was decreed for him on Rosh Hashanah. And the end of the matter will be that the money of [i.e., attained by] the wrong will consume also the "surviving remnant," the "kosher" grant that had already been allotted him. As Chazal have said (Succah 29b): "Because of four things a man's property goes lost," one of them being because he divests himself of his own yoke and places it on his friend. And so we find in Derech Eretz Zuta, Chapter 3: "If you have taken what is not yours, yours will be taken from you." And he will remain only with the bartering of a kosher grant for one that is forbidden. For he will be destined to give din and accounting for every [misappropriated] p'rutah [small coin]. As Chazal have said (Bava Kamma 119a): "If one steals from his friend the worth of a p'rutah, it is as if he has taken his soul." And he also constrains the Holy One Blessed be He to return the theft to its owner. As Chazal have said (Sanhedrin 8a): "The Holy One Blessed be He says to the wicked: 'It is not enough that you steal, but you also constrain Me to return the theft to its owner." And all of these things are intimated in our holy Torah, in Parshath Vayetze, where it is written (Bereshith 32:11-12): "And the angel of the L-rd said to me in a dream: 'Yaakov, … lift up your eyes and see all the rams that go up on the sheep — ringstraked, speckled and grizzled" (As Rashi explains there, the angels would bring them from the flock assigned to the sons of Lavan to that assigned to Yaakov. And lest you ask, how am I permitted to take from the grant of Lavan and give it to you? The angel, therefore, concludes: "For I have seen all that Lavan does to you," that he has changed your wage ten times and taken your grant; therefore I am returning it to you.)]

The Sages also stated: "if one steals from his fellow even the worth of a peruta (small coin), it is as if he takes his life from him" (Bava Kama 119a). This teaching reveals to us, the graveness of this sin even for a small amount. They further said: "the rains are withheld only because of the sin of theft" (Taanit 7b). And "for a basketful of sins, which sin prosecutes at the head of all of them? - theft" (Vayikra Raba 33:3). And "the generation of the flood had their fate sealed only because of the sin of theft" (Sanhedrin 108a).