Who were the Levites and what did they do?

Numbers 1:50, The Levites. The role of the Levites was to assist the priests in the tabernacle service (Num 3:6–8; 16:9; 1 Chr 23:28–32; Ezra 3:8) including caring for the tabernacle (Num 1:53) and its furniture, its setting up, dismantling and transporting (Num 3–4). In addition, they assisted the priests by preparing the cereal offering (1 Chr 23:29). They acted as singer and musicians in the temple to offer praise to YHVH (1 Chr 23:30). They were allowed to approach the tabernacle furniture only after the priests had covered and prepared them for transport (Num 4:5–15; 18:3) but they could not touch any of the tabernacle’s set-apart instruments lest they die (Num 4:15), nor could they even see them (Num 4:20).

Not only were the Levites commissioned to attend to the needs of the priests and the things of the tabernacle, but YHVH instructed them “to attend to the needs” or “keep charge” (Heb. mishmereth) of, presumably, the spiritual needs of the whole congregation or children of Israel (Num 3:7–8). Although mishemereth is a noun meaning “charge, function, obligation, service, or watch,” it is often translated into English as a verbs of action such as “to keep, guard, keep charge, or watch” through its root shamar, a verb meaning “to keep, guard, observe, give heed.” Mishmereth principally refers to the Levites’ obligatory duties relating to the service of the temple.

Later on, the Levites were involved in teaching and interpreting the Torah (Neh 8:7, 9; 2 Chr 17:7–9; 35:3). There is no indication that the Levites were permitted to offer sacrifices, with the notable exception of Samuel, who was a Levite, but not a priest (1 Sam 1:1 cp. 1 Chr 6:28).

YHVH chose the Levites as his set-apart ministers to replace the firstborn of the Israelites that he spared when he smote the firstborn of the Egyptians (Num 3:12–13, 41–45).