John Wesley on 2 Chronicles 29:21

Seven - 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 done by the people, there was but one bullock to be offered, but here the sins were many and presumptuous. Kingdom - To make atonement for the sins of the king and the royal family, and the court. Sanctuary - For all the idolatry and uncleanness wherewith the temple had been polluted. 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 thro' Christ, who was made sin, that is, a sin - offering for us.