Charles Ellicott Commentary Deuteronomy 15:5

"if only thou diligently hearken unto the voice of Jehovah thy God, to observe to do all this commandment which I command thee this day." — Deuteronomy 15:5 (ASV)

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.