Albert Barnes Commentary Deuteronomy 14:28-29

"At the end of every three years thou shalt bring forth all the tithe of thine increase in the same year, and shalt lay it up within thy gates: and the Levite, because he hath no portion nor inheritance with thee, and the sojourner, and the fatherless, and the widow, that are within thy gates, shall come, and shall eat and be satisfied; that Jehovah thy God may bless thee in all the work of thy hand which thou doest." — Deuteronomy 14:28-29 (ASV)

Compare the marginal references. The tithe thus directed in the third year to be dispensed in charity at home, was not paid in addition to that in other years bestowed on the sacred meals, but was substituted for it.

The three years would count from the sabbatical year (see the next chapter), in which year there would of course be neither payment of tithe nor celebration of the feasts at the sanctuary. In the third year and sixth year of the septennial cycle the feasts would be superseded by the private hospitality enjoined in these verses.