In a book - in the book, i. e. the book which contained the history of God’s dealings with His people. Moses was further instructed to impress the command especially on the mind of Joshua, as the leader to whom the first step toward its accomplishment would be entrusted on the conquest of Canaan. The work was not actually completed until the reign of Hezekiah, 1 Chronicles 4:43.
Related Commentaries of Exodus 17:14
Exodus 17:14
14 And the LORD said unto Moses, Write this for a memorial in a book, and rehearse it in the ears of Joshua: for I will utterly put out the remembrance of Amalek from under heaven.