2 Chronicles 29:21 - Joseph Benson’s Commentary on the Old and New Testaments

They brought seven bullocks The number seven is customary in sacred matters, and is here used in regard of the vast numbers and various kinds of sins, the guilt whereof yet lay upon the kingdom, which was now to be expiated. Indeed, in case of one particular sin of ignorance committed by the people, there was but one bullock to be offered, but here the sins were many and presumptuous. For a sin-offering for the kingdom To make atonement for the sins of the king, and the royal family, and the court. And for the sanctuary For all the idolatry and uncleanness wherewith the temple had been polluted, which, as it had been cleansed naturally by the priests' hands, so now it was to be purged morally by sacrifices. And for Judah For the sins of all the people of Judah. They thought it not enough to lament and forsake their sins, but they brought a sin-offering. Even our repentance and reformation will not obtain pardon, but through Christ, who was made sin, that is, a sin-offering, for us.