Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

Every third year, on the other hand, they were to separate the whole of the tithe from the year's produce ("bring forth," sc., from the granary), and leaven it in their gates (i.e., their towns), and feed the Levites, the strangers, and the widows and orphans with it. They were not to take it to the sanctuary, therefore; but according to Deu 26:12., after bringing it out, were to make confession to the Lord of what they had done, and pray for His blessing. "At the end of three years:" i.e., when the third year, namely the civil year, which closed with the harvest (see at Exo 23:16), had come to an end. This regulation as to the time was founded upon the observance of the sabbatical year, as we may see from Deu 15:1, where the seventh year is no other than the sabbatical year. Twice, therefore, within the period of a sabbatical year, namely in the third and sixth years, the tithe set apart for a sacrificial meal was not to be eaten at the sanctuary, but to be used in the different towns of the land in providing festal meals for those who had no possessions, viz., the Levites, strangers, widows, and orphans. Consequently this tithe cannot properly be called the "third tithe," as it is by many of the Rabbins, but rather the "poor tithe," as it was simply in the way of applying it that it differed from the "second" (see Hottinger, de decimies, exerc. viii. pp. 182ff., and my Archol. i. p. 339). As an encouragement to carry out these instructions, Moses closes in Deu 14:29 with an allusion to the divine blessing which would follow their observance.