Charles Ellicott Commentary 2 Kings 23:21

"And the king commanded all the people, saying, Keep the passover unto Jehovah your God, as it is written in this book of the covenant." — 2 Kings 23:21 (ASV)

Keep the passover. — Hold a passover (2 Kings 23:22). (Compare to 2 Chronicles 35:1–19 for a more detailed account of this unique celebration.) Josiah had the precedent of Hezekiah for signaling his religious revolution by a solemn passover (2 Chronicles 30:1).

In the book of this covenant. —Rather, in this book of the covenant (2 Kings 23:2). The book was that which Hilkiah had found in the Temple, and which gave the impulse to the whole reforming movement. (The Septuagint and Vulgate read, in the book of this covenant —a mere mistake.)