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.

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.

And the Lord said unto Moses,.... After the battle was over, and the Israelites had got the victory:

write this for a memorial in a book: not in loose papers, but in a book, that it might continue; meaning that the account of this battle with Amelek should be put down in the annals or journal of Moses, in the book of the law he was writing, or was about to write, and would write, as he did, see Joshua 1:7 that so it might be kept in memory, and transmitted to the latest posterity; it being on the one hand an instance of great impiety, inhumanity, and rashness, in Amalek, and on the other a display of the goodness, kindness, and power of God on the behalf of his people: and

rehearse it in the ears of Joshua; who was a principal person concerned in this battle, and therefore, when the account was written and rehearsed, could bear witness to the truth of it, as well as he was to be the chief person that should be concerned in introducing the Israelites into the land of Canaan, and subduing the Canaanites; and therefore this, and what follows, was to be rehearsed to him, as the rule of his conduct toward them, and particularly Amalek:

for I will utterly put out the remembrance of Amelek from under heaven; so that they shall be no more a nation, and their name never mentioned, unless with disgrace and contempt. This was fulfilled partly by Saul, 1 Samuel 15:8 and more completely by David, 1 Samuel 30:17, and the finishing stroke the Jews give to Mordecai and Esther, as the Targum of Jerusalem on Exodus 17:6.

As this battle and victory were of such significance, Moses was to write it for a memorial בּסּפר, in "the book" appointed for a record of the wonderful works of God, and "to put it into the ears of Joshua," i.e., to make known to him, and impress upon him, that Jehovah would utterly put out the remembrance of Amalek from under heaven; not "in order that he might carry out this decree of God on the conquest of Canaan, as Knobel supposes, but to strengthen his confidence in the help of the Lord against all the enemies of Israel. In Deuteronomy 25:19 the Israelites are commanded to exterminate Amalek, when God should have given them rest in the land of Canaan from all their enemies round about.

And the LORD said unto Moses, Write this for a memorial {h} in a book, and rehearse it in the ears of Joshua: for I will utterly put out the remembrance of Amalek from under heaven.

(h) In the book of the law.

14-16. Write this for a memorial-If the bloody character of this statute seems to be at variance with the mild and merciful character of God, the reasons are to be sought in the deep and implacable vengeance they meditated against Israel (Ps 83:4).

17:8-16 Israel engaged with Amalek in their own necessary defence. God makes his people able, and calls them to various services for the good of his church. Joshua fights, Moses prays, both minister to Israel. The rod was held up, as the banner to encourage the soldiers. Also to God, by way of appeal to him. Moses was tired. The strongest arm will fail with being long held out; it is God only whose hand is stretched out still. We do not find that Joshua's hands were heavy in fighting, but Moses' hands were heavy in praying; the more spiritual any service is, the more apt we are to fail and flag in it. To convince Israel that the hand of Moses, whom they had been chiding, did more for their safety than their own hands, his rod than their sword, the success rises and falls as Moses lifts up or lets down his hands. The church's cause is more or less successful, as her friends are more or less strong in faith, and fervent in prayer. Moses, the man of God, is glad of help. We should not be shy, either of asking help from others, or of giving help to others. The hands of Moses being thus stayed, were steady till the going down of the sun. It was great encouragement to the people to see Joshua before them in the field of battle, and Moses above them on the hill. Christ is both to us; our Joshua, the Captain of our salvation, who fights our battles, and our Moses, who ever lives, making intercession above, that our faith fail not. Weapons formed against God's Israel cannot prosper long, and shall be broken at last. Moses must write what had been done, what Amalek had done against Israel; write their bitter hatred; write their cruel attempts; let them never be forgotten, nor what God had done for Israel in saving them from Amalek. Write what should be done; that in process of time Amalek should be totally ruined and rooted out. Amalek's destruction was typical of the destruction of all the enemies of Christ and his kingdom.