In the eighteenth year of Josiah’s reign, this Passover was observed.
The destruction which Josiah made of idols and idolatry was more largely related in the Kings, but just mentioned here in the foregoing chapter (v. 33); but his solemnizing the passover, which was touched upon there (Kg2 23:21), is very particularly related here. Many were the feasts of the Lord, appointed by the ceremonial law, but the passover was the chief.
Commenting on 2 Chronicles 35:1-19
In the eighteenth year of the reign Josiah was this passover kept--"It is said (Kg2 22:3) that Josiah sent Shaphan to Hilkiah in the eighth month of that year." If this statement rests upon an historical basis, all the events narrated here (at 2Ch. 34:8-35:19) must have happened in about the space of five months and a half.
In the eighteenth year of the reign of Josiah was this passover kept. (i) Which was in his 26th year.