Halakhah su Deuteronomio 23:20

That He prohibited us from having weights and measures that are deficient, with us in our homes - even though one does not buy and sell with them. And that is His, may He be exalted, saying, "You are not to have for yourself in your pouch varying weight-stones, large and small" (Deuteronomy 25:13); and likewise, "varying ephah measurements" (Deuteronomy 25:14). And the language of the Gemara, Batra (Bava Batra 89b), is, "It is prohibited for a person to keep in his house a measure that is deficient or inflated, even if [he only uses it as] a chamber pot for urine." And you should not think that His saying, "You are not to have for yourself [...] "varying ephah measurements"; and "You are not to have for yourself [...] varying weight-stones" - [signifies] that they are two [distinct] negative commandments. Indeed, it is coming to round out the laws of the commandment, so that the types of measures are explained - and they are weight and measurement. It is as if He would say, "You should not have two measures with you - not for measuring, and not for weighing," as we explained in the Positive Commandments (Sefer HaMitzvot, Positive Commandments 208). And His saying, "You are not to have for yourself [...] varying weight-stones"; and "You are not to have for yourself [...] varying ephah measurements" - is like His saying, "You shall not charge interest to your brother; interest of money, interest of food, interest of anything upon which interest can be charged" (Deuteronomy 23:20) - which is one negative commandment that includes many types, all of which have the very same content. And it is not from the repetition of language that there is an expansion of commandments, as we discussed earlier in Principle 9. And something like this negative commandment already came before us; and that is His saying, ""no chametz may be seen [...], and no leaven may be seen" (Exodus 13:7). (See Parashat Ki Tetzei; Mishneh Torah, Theft 7.)

That the borrower not give interest to an Israelite: That we have been prevented from giving interest to an Israelite (see Sefer HaMitzvot LaRambam, Mitzvot Lo Taase 236), and, so too, from taking it. And about this is it stated (Deuteronomy 23:20), "You shall not take interest from your brother, interest of money, interest of food, interest of any thing, etc". And the [traditional] explanation comes about this: "Do not take interest" means, do not have interest taken from you, which is to say, do not give interest - as the one who gives it is the one who has it taken from him. And in the elucidation, they said in the chapter [entitled] Eizehhu Neshekh (Bava Metzia 75b) [that] the borrower transgresses on "Do not take interest" and on "you shall not place a stumbling block before the blind" (Leviticus 19:14). And had this preventing of this not come explicitly, I would have reasoned that it is the lender that is forbidden from taking it, but [that] if the borrower wants to forgive and is willing to be oppressed, that it would be permitted - in the manner of [other] oppression, where it is the oppressor that is transgressing, not the oppressed.

And Rambam wrote (Sefer Hamitzvot LaRambam, Mitzvot Lo Taase 272), "And do not think that they are two [distinct] commandments since they are two negative statements [in the Torah]. Indeed, [the two statements] have come to complete the laws of the commandment, such that two types of size are included - and they are the weight and the measure. [It is] as if it stated, 'You should not have two sizes, not in measurement and not in weight.' [It is] like 'You shall not take interest from loans to your brother, whether in money or food or anything else that can be taken as interest' (Deuteronomy 23:20) - which is all one negative commandment. As it is not by the duplication of expressions that [the number of] commandments increase, when it is all one matter. And so [too with] 'no leavened bread shall be found with you, and no leaven shall be found' (Exodus 13:7), which is [all] one negative commandment, since it is [all] one matter. Rather, [the two expressions] are stated to complete the elucidation of the matter."