(5) Only if thou carefully hearken.—“Then there will be none among thee in want.” So Rashi expounds, in the very spirit of the passage in Acts 4.

15:1-11 This year of release typified the grace of the gospel, in which is proclaimed the acceptable year of the Lord; and by which we obtain the release of our debts, that is, the pardon of our sins. The law is spiritual, and lays restraints upon the thoughts of the heart. We mistake, if we think thoughts are free from God's knowledge and check. That is a wicked heart indeed, which raises evil thoughts from the good law of God, as theirs did, who, because God had obliged them to the charity of forgiving, denied the charity of giving. Those who would keep from the act of sin, must keep out of their minds the very thought of sin. It is a dreadful thing to have the cry of the poor justly against us. Grudge not a kindness to thy brother; distrust not the providence of God. What thou doest, do freely, for God loves a cheerful giver, 2Co 9:7.There is no inconsistency between this and Deuteronomy 15:11. The meaning seems simply to be, "Thou must release the debt for the year, except when there be no poor person concerned, a contingency which may happen, for the Lord shall greatly bless thee." The general object of these precepts, as also of the year of Jubilee and the laws respecting inheritance, is to prevent the total ruin of a needy person, and his disappearance from the families of Israel by the sale of his patrimony.4. Save when there shall be no poor man among you—Apparently a qualifying clause added to limit the application of the foregoing statement [De 15:3]; so that "the brother" to be released pointed to a poor borrower, whereas it is implied that if he were rich, the restoration of the loan might be demanded even during that year. But the words may properly be rendered (as on the Margin) to the end, in order that there may be no poor among you—that is, that none be reduced to inconvenient straits and poverty by unseasonable exaction of debts at a time when there was no labor and no produce, and that all may enjoy comfort and prosperity, which will be the case through the special blessing of God on the land, provided they are obedient. No text from Poole on this verse.

In his word, and by his prophets; this being the case, there would be no more poor among them, or however they would be so blessed of God, that they would be capable of releasing the debts of the poor, without hurting themselves and their families:

to observe to do all these commandments which I command thee this day; a phrase often used to put them in mind of the commands of God, and the necessity of keeping them, their temporal happiness depending thereon.

Only if thou carefully hearken unto the voice of the LORD thy God, to observe to do all these commandments which I command thee this day.