John Calvin Commentary Deuteronomy 18:6

"And if a Levite come from any of thy gates out of all Israel, where he sojourneth, and come with all the desire of his soul unto the place which Jehovah shall choose;" — Deuteronomy 18:6 (ASV)

And if a Levite come. This third point more clearly explains what is elsewhere more obscurely declared, for God seemed to withhold from the Levites whatever He gave to the priests. But He now more distinctly places the priests in the first rank, yet in such a way that they should admit the Levites, in recognition of their labors, to a share of the offerings. This is the essence of the law: that the Levites who remained at home should be content with the tithes and touch nothing of the other offerings; but that wherever they should come to the sanctuary, they were to be regarded as ministers and take their proper place.

By this law, then, it was provided that none should be excluded on the ground of an interruption of their duties, and that the condition of those who lived elsewhere should not be worse than that of those who lived at Jerusalem. For although they might reside in other cities, they did not entirely cease from their ministry, since they had other duties to perform besides that of sacrificing the victims.

Yet those who entirely devoted themselves to the work of the sanctuary were endowed by God with double honor, since it was by no means just that they should be defrauded of their maintenance, who gave up domestic cares and labors and occupied themselves entirely with holy duties. That this distribution was not unnecessary will be most evident from the narrative of Josephus, who relates that the ²²⁶ priests seized the tithes by violence and deprived the Levites of their livelihood by hostile measures.

²²⁶ About this time King Agrippa gave the high priesthood to Ismael, who was the son of Fabi. And such was the impudence and boldness that had seized on the high priests, that they had the hardiness to send their servants into the threshing-floors, to take away those tithes that were due to the priests; insomuch that it so fell out that the poorer sort of the priests died for want.” — Whiston’s Josephus. Antiq. 20 ch. 8, sec. 8. See also ch. 9, sec. 2.