Halakhah zu Dewarim 15:9

It is a positive Biblical command to give Charity according to one's means. There are numerous positive commands as to Charity; and also a negative command not to close one's eyes to charity, for it is written, "Thou shalt not harden thy heart nor shut thy hand [from thy poor brother]."¹Deut. 15:7. And he who closes his eyes to it is called "wicked"²The word is Beliya’al, which occurs in Deut. 15:9. and is regarded as if he worships idols. One should take great heed in giving alms that he be not the cause of bloodshed, for the poor man in need may die before help reaches him if it is not offered quickly, as in the story of Nahum of Gimzo.³Ta’anith 21. (A treatise of the Talmud.)

And [also] included in this commandment is that a person should not have cling to his money that God has graced him with justly, other money that is from theft, extortion, interest or from any ugly thing; since all of this is included in the auxiliaries of idolatry. As the evil impulse of a man's heart desires it and brings it to his house - and the evil impulse is called by the name, idolatry; and like they, may their memory be blessed, said (Bava Batra 10a) that about it is it stated (Deuteronomy 15:9), "lest there be a wanton thing with your heart," and it is written about the matter of idolatry (Deuteronomy 13:14), "Wanton men have gone out from you and have induced, etc." And about monies like this that we mentioned and about the auxiliaries of idolatry - about all of them - is it stated (Deuteronomy 7:26), "and you will be an anathema like it"; meaning to say that all that clings to it is anathema. As the blessing of God is not found in it, and [so] it disappears and is lost; like the matter that they, may their memory be blessed, said (Bava Metzia 71a) that a small coin of interest makes several treasuries of money disappear. As this comes and destroys that.

To not refrain from lending before the sabbatical year: To not refrain from lending to those that need, due to fear of the sabbatical year, that it not remove the debt. And about this is it stated (Deuteronomy 15:9), "Guard yourself, lest there be a wanton thing in your heart saying, 'The sabbatical year is approaching.'" And the language of Sifrei Devarim 117 is "'Guard yourself' as a negative commandment; 'lest there be' as a negative commandment" - meaning to say that these two negative commandments come about this matter, one after the other to strengthen [it].