Deuteronomy 23:20

Thou shalt not make usury of that which is thine from thy neighbour upon the loan which thou lendest, either of money, or food, or any thing by which thou mayest make usury.

you must not utilize interest with your brother Having mentioned the non-Jewish slave, Scripture must now elucidate that you are permitted to charge him interest, even though it says, concerning him, “you must not oppress him” [: 17].

you must not utilize interest with your brother There is a difference between “charge interest” and “utilize interest”: The latter means that you may not even accept interest from your brother who offers it to you (who would also be guilty of violating the interest prohibition). The verb takes both a direct and an indirect object. Others say that “utilize interest” is the same as “charge interest”, and there is no difference between the two words.

LO THASHICH form tashich is understood in a causative sense as meaning: “Thou shalt not cause thy brother to take interest.” See “The Commandments,” Vol. II, pp. 224-225. L’ACHICHA’ (THOU SHALT NOT CAUSE THY BROTHER TO TAKE INTEREST). This also is an explanatory commandment, adding here an admonition to the borrower as well, unlike all civil cases, for if a person wishes to damage his belongings he may do so [and it should, therefore, be permitted to the borrower to give freely to the lender]. However, because of the habitual nature of this sin [of giving interest], Scripture admonishes the borrower as well. And he explained here that a heathen’s interest is permissible. This he did not mention with reference to robbery and theft, as the Rabbis have said. “Theft from a heathen is forbidden.” But borrowing for interest, which is agreed upon by both parties and is done voluntarily, was forbidden [by the Torah] only because of brotherliness and kindness, as He commanded, and thou shalt love thy neighbor as thyself, and as he said, Beware that there be not a base thought in thy heart etc. [and thine eye be evil against thy needy brother, and thou give him nought]. Therefore he said [here], that the Eternal thy G-d may bless thee, for it is an act of mercy and compassion that one does for his brother by lending him without interest, and it will be accounted to him for righteousness. The release of debts [in the Seventh year] is also an act of mercy among brothers, and therefore he said, Of a foreigner thou mayest exact it, and for him [who releases the debt of a brother] he designated a blessing,, Verse 4. for Scripture mentions a blessing only in connection with charity and acts of mercy, and not for [the mere abstention from] robbery, theft, and fraud.
He mentions interest of money, interest of victuals in order to explain that he who lends one measure of wheat for a measure and a half is [guilty of taking] true interest even if at the time of payment a measure and a half is not worth as much as was the one measure that he lent him. And he further explained, interest of any thing that is lent upon interest, meaning even building-blocks and other articles which are lent. For it might occur to one to think that “interest” applies only to money with which everything can be purchased and to victuals which sustain life, but in other things we should go according to the cash value at the time of the loan and the repayment [therefore Scripture prohibited all such interest expressly]. Now our Rabbis have interpreted 263. See also Ramban above 15:3 where this subject is explained more fully. the verse, Unto a foreigner thou shalt lend upon interest as being a negative commandment derived from a positive commandment [which carries the force of a positive commandment] with respect to lending to an Israelite. [They rendered this interpretation] because the verse is redundant, for he already stated ‘lo thashich’ thy brother [which implies clearly that it is permitted to exact interest from a foreigner; why then the repetition, Unto a foreigner etc.? It was to teach that an interest-bearing loan to an Israelite is in violation of both a negative and a positive commandment].

לא תשיך, according to the plain meaning the Torah speaks of the lender.

לא תשיך לאחיך, after warning us concerning behaviour the result of which is G’d’s withdrawing His benevolent presence from the Jewish people, He cautions us concerning the acts of loving kindness which would ensure the continued presence of His Shechinah. Two major steps in that direction are: 1) not to charge a fellow Jew interest on a loan extended to him, 2) not to be tardy in discharging the obligations assumed when making a vow in favour of G’d. (verse 22) These include vows representing donations to charity which are due without delay, seeing that there is never a shortage of people in need who have to be supported by charity.
Then there is the subject of what a labourer may eat when he is surrounded by fruit belonging to his employer, as well as the matter of divorce, something that must not be given to a woman unless she has been guilty of a serious misdemeanour, i.e. ערות דבר. (24,1) A major reason for granting a divorce is the effort to prevent bastards from being born. No other reason is considered as valid to divorce one’s wife, the prophet Maleachi 2,14 reminding people that at least G’d will testify against the husband who dealt treacherously with the wife he married in his youth and now abandoned.
The loving kindness performed with a newly wed (betrothed) woman is that her husband is given a chance to fulfill the commandment of making his bride joyful during the first year of their marriage. (24,5). The prohibition against taking as a pledge, i.e. collateral for overdue debts, tools needed for the debtor to make his living, such as millstones is self-evident. (24,6) Precautions against potential hazards that could hurt many people, prohibition against kidnappers coupled with the death penalty is a preventive measure, i.e. an act of kindness designed to protect parents against their children becoming the victims of such “stealing.” The isolation of people afflicted with the skin disease known as tzoraat, is all too well known. It not only prods the victim to mend his asocial behaviour, but it protects society at the same time. Cautions against tale-bearing and other forms of abuse of the power of speech are acts of kindness in respect of the potential victims of such slander. Not muzzling an ox while he threshes, is a show of understanding for the ox’s feelings in helping to provide food for its owner while himself being denied that same food. Etc. Etc.