Charles Ellicott Commentary 2 Chronicles 29:34

"But the priests were too few, so that they could not flay all the burnt-offerings: wherefore their brethren the Levites did help them, till the work was ended, and until the priests had sanctified themselves; for the Levites were more upright in heart to sanctify themselves than the priests." — 2 Chronicles 29:34 (ASV)

Flay all the burnt offerings. — In private offerings this was done by the worshipper himself (Leviticus 1:6). In national sacrifices it appears to have been the duty of the priests.

Did help them. — See margin; and Ezra 6:22.

Until the other priests had sanctified. — Began to sanctify themselves, as a body.

For the Levites ... in heart. — The priests, as a class, were probably more deeply involved in the corruption of the last reign.