Adam Clarke on 2 Chronicles 29:21

They brought seven bullocks, etc. - This was more than the law required; see Lev 4:13, etc. It ordered one calf or ox for the sins of the people, and one he-goat for the sins of the prince; but Hezekiah here offers many more. And the reason appears sufficiently evident: the law speaks only of sins of ignorance; but here were sins of every kind and every die - idolatry, apostasy from the Divine worship, profanation of the temple, etc., etc. The sin-offerings, we are informed, were offered, first for the Kingdom - for the transgressions of the king and his family; secondly, for the Sanctuary, which had been defiled and polluted, and for the priests who had been profane, negligent, and unholy; and, finally, for Judah - for the whole mass of the people, who had been led away into every kind of abomination by the above examples.