Charles Ellicott Commentary 2 Chronicles 30:3

"For they could not keep it at that time, because the priests had not sanctified themselves in sufficient number, neither had the people gathered themselves together to Jerusalem." — 2 Chronicles 30:3 (ASV)

At that time. —The time when the Temple had just been reopened (2 Chronicles 29:8), in the first month of Hezekiah’s first year. The Purification of the Temple was not completed until the 16th of Nisan (2 Chronicles 29:17); but perhaps the Passover would have been held, had not the hindrances here mentioned prevented it. (See 2 Chronicles 29:34).

Sufficiently. — Lĕmaddày. Literally, unto what was enough (lĕ-mah-dày), an expression only found here. (Compare a similar formation, 1 Chronicles 15:13.) The meaning is that a sufficient number of priests had not observed the legal ceremonies of self-purification in time to hold Passover in Nisan.