John Gill Commentary Deuteronomy 15:10

"Thou shalt surely give him, and thy heart shall not be grieved when thou givest unto him; because that for this thing Jehovah thy God will bless thee in all thy work, and in all that thou puttest thy hand unto." — Deuteronomy 15:10 (ASV)

You shall surely give him
Or lend to him; though lending in such a case and circumstances, that person being extremely poor, and the year of release at hand, is the same as giving. Jarchi remarks that money must be given him, even a hundred times if he asks it; but the limitation is to what he wants, and what is sufficient for his present wants, (Deuteronomy 15:8)

and your heart shall not be grieved when you give unto him ;
grieved at parting with his money he has little or no hope of seeing again, grudging it to him to whom it is given; when, on the other hand, it should be given freely and cheerfully, for God loves a cheerful giver:

because that for this thing the Lord your God shall bless you in all
your works, and in all you put your hand unto ;
that is, for lending or giving largely, liberally, and cheerfully, to persons in distress; see (Proverbs 11:24Proverbs 11:25) (Isaiah 32:8) (2 Corinthians 9:6–9) .