Deuteronomy 17:9

9. Thou shalt come unto the priests the Levites It is claimed that this book was not written by the same author as the earlier books, because in them the term used is, the priests the sons of Aaron.” In Deuteronomy they are never called the sons of Aaron, but the sons of Levi, or the Levites.

The difference of time in the composition of Leviticus and Deuteronomy is sufficient to account for the different term. When Leviticus was written Aaron was alive. When the discourses of Deuteronomy were spoken Aaron was dead, and the priests would have acquired a position for themselves. It is suggested by Wordsworth, in his Commentary on this passage, that it was very natural that “Moses, now about to depart, should desire to appease all jealousies between priests and Levites; and for this purpose he could not use a more healing phrase than that now before us, the priests the Levites. For thus on the one hand he exhorted the priests to treat the Levites with kindness as brethren, and not to domineer over them; and on the other hand he cheered the Levites with the reflection that the priests were of the same origin as themselves; that they therefore themselves derived honour from the priestly dignity, and ought not to encroach upon it, but to feel themselves honoured by being permitted to assist those who were invested with it.” For a thorough and exhaustive treatment of this question the reader is referred to CURTISS’S Levitical Priests.