Or HaChaim on Leviticus 19:13/אור החיים על ויקרא י״ט:י״ג

1 לא תעשוק את דעך, "Do not oppress your fellow Jew." After the Torah had forbidden the acquisition of someone else's money through theft a person might conclude that the Torah's objection is only to thievery and not to other ways of appropriating something which is rightfully someone else's. This is why the Torah had to outlaw the obtaining of money by someone exploiting his position of strength vis-a-vis a person whose social or financial position places him at a disadvantage. The prohibition includes withholding wages of a labourer even only for one night.

2The reason the Torah describes the injured party as רע, a colleague or friend, is to warn us not to presume on the other party's friendship towards us to shortchange them in what is due to them. One must not play loose with a friend's money because he is one's friend and presumably will not voice his objection for the sake of preserving the friendship. The word את רעך is justified seeing the subject is one which involves only people, not G'd directly. Moreover, if the friend forgives the harm done to him such behaviour is not considered a sin vis-a-vis G'd.

3A moral-ethical dimension of these verses is found in Berachot 35 where the Talmud discusses Proverbs 28,24: "he who robs father or mother saying it is no sin is a companion of a destroyer." The Talmud views the verse as referring to someone enjoying the products of this world without first reciting a benediction acknowledging that it all belongs to G'd. Father and mother in that verse are supposed to be G'd and the concept of the people of Israel, commonly referred to as כנסת ישראל. The word רעך in our verse would refer to G'd Himself. We are entitled to this homiletical approach based on Proverbs 27,10 where Solomon warns not to abandon "your friend and the friend of your father." This means one should not "rob" G'd of what He provides without first acknowledging it, taking permission, so to speak. The reason the Torah adds the words "do not rob," is to tell you that even the paucity of מצוה-performance contains an element of robbery. When one fails to carry out a commandment which one is obligated to observe and has the opportunity to observe one causes harm to the entire Jewish people, i.e. one is guilty of transgressing the commandment לא תלין, not performing one's duty on time. When the Torah writes: "do not keep overnight with you the wages due to a labourer," this is a demand to perform daily and punctually in one's מצוה-performance. Vayikra Rabbah 26,4 describes the practice of day borrowing from night during the summer months, whereas night borrows from day during the winter months. [ideally, both day and night should be 12 hours long all year long were it not for the fact that the earth's axis is (nowadays, since the deluge) at an angle. Ed.] The Midrash presents this as an ideal way of two parties helping each other out without recourse to written contracts, demands for repayment, etc. When the Torah writes לא תלין פעולת שכיר אתך, "do not hold back the wages of your labourer with you all night long," the word אתך, refers back to the word שכיר, "someone hired by G'd," a reference to the spirit G'd has granted His labourers, i.e. man. G'd looks upon man as His hired hand. He has granted this spirit both to the hired hand as well as to the resident. Man's wages are that he is granted the privilege to carry out the commandments of G'd. Anyone of us failing to do so or doing so belatedly harms the whole people.

4This verse also contains an allusion to the well known statement by our sages (Berachot 28) that Torah scholars do not find much sustenance in this life. We also have a Yalkut Shimoni (item 934 on Proverbs) on Proverbs 3,3 which appears to promise much temporal reward for Torah study. The Torah is supposed to have wanted to know why people studying it are usually so poor. I have heard a good answer to this question in the name of the Ari Zal. He explained that the physical universe we live in would be unable to absorb all the goodness G'd would have to bestow on the Torah scholars. G'd therefore decided to bestow such goodness only on the average individuals who in turn are charged with looking after the material needs of the Torah scholars. This teaches that the only reason there are apparently undeserving wealthy people in this world is that they serve as a מרזב, a channel to furnish sustenace to the Torah scholars. G'd has commanded here that that a (wealthy) person must not oppress a Torah scholar by withholding the material benefits from him which it is his function to provide for his רע, his friend, the Torah scholar.

5The word את in the verse לא תעשוק, next to the word רעך, -a reference to G'd as we explained,- is to be understood as similar to what Rabbi Akiva explained in Pessachim 22. In that instance Rabbi Akiva explains the word את in את ה׳ אלוקיך תירא as referring to Torah scholars. The Torah intended to warn us to revere Torah scholars, the judges, in much the same manner as we revere G'd Himself. Judges are also known as אלהים, so that we can say the Torah warns not to steal or rob as G'd has representatives on earth who will deprive the thief or robber of whatever he has taken unlawfully.