פירוש על דברים 18:6

וכי יבא הלוי AND IF A LEVITE COME […AND MINISTER] — One might think that Scripture speaks of a “Levite” in the usual sense of the word (i.e. of a לוי and not of a כהן)! Scripture, however, goes on to state, (v. 7) “And he shall minister [in the name of the Lord]”; thus the Levites must be excluded for they are not fit for (not entitled to) service in the Temple (Sifrei Devarim 168:1).

וכי יבא הלוי, a priest who does not belong to the roster of priests performing Temple service on that day in the courtyard of the Temple in Jerusalem

Perhaps it is literally to the Levite that Scripture refers?, etc. I.e. an actual descendant of Levi, to exclude a kohein. Or perhaps the verse includes a kohein also, because a kohein is also a descendant of Levi? [In proof of this latter suggestion] the Torah therefore teaches, “He shall perform the service,”, etc.