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. Write this for a memorial in a book - This is the first mention of writing on record: what it signified, or how it was done, we cannot tell. But it is evident that either this passage is introduced here instead of Deuteronomy 25:17, by way of anticipation, or that by the words כתב שפר kethob and sepher was intended only a monumental declaration of the defeat of Amalek by Joshua, by some action or symbolical representation; for it is immediately subjoined, "And Moses built an altar, and called the name of it Jehovah-nissi." See Dr. A. Bayley, and see the note on Exodus 30 (note). It is very likely that the first regular alphabetical writing in the world was that written by the finger of God himself on the two tables of stone. What is said here was probably by way of anticipation, or means some other method of registering events than by alphabetical characters, if we allow that God gave the first specimen of regular writing on the tables of stone, which did not take place till some time after this.
Rehearse it in the ears of Joshua - Thus showing that Joshua was to succeed Moses, and that this charge should be given to every succeeding governor.
I will utterly put out the remembrance of Amalek - This threatening was accomplished by Saul, 1 Samuel 15:3, etc.; four hundred and twelve years after. Judgment is God's strange work; but it must take place when the sins which incensed it are neither repented of nor forsaken. This people, by their continued transgressions, proved themselves totally unworthy of a political existence; and therefore said God to Saul, Go, and utterly destroy the Sinners the Amalekites; 1 Samuel 15:18. So their continuance in sin was the cause of their final destruction.