For the source text click/tap here: Yevamot 86
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The Gemara quotes Rebbi Yehoshua ben Levi who says that in 24 places the Torah refers to Kohanim as "Leviyim." RASHI in Chulin (24b) suggests that they are called "Leviyim" because they perform the Avodah in the Beis ha'Mikdash, as the word "Levi" also means "those who help serve" (as in Bamidbar 18:2). The Gemara cites one example of such a verse (Yechezkel 44:15).
What are the other 23 places in which the Torah refers to Kohanim as "Leviyim"? The Acharonim discuss this question and have great difficulty identifying all 24 places.
The BEN YEHOYADA in Bechoros (4b) writes that he searched and found only eleven places where the word "Leviyim" refers to Kohanim and not to Leviyim. However, RAV DAVID COHEN shlit'a (in OHEL DAVID, end of volume 1) writes that he counted the places where the word "Leviyim" refers either to Kohanim by themselves or to Kohanim and Leviyim together, and he found 76 places where the Torah refers to Kohanim as "Leviyim.”
We explore the history and scholarship on the levitical priesthood and how it developed