Exodus 17:16

"And he said, Jehovah hath sworn: Jehovah will have war with Amalek from generation to generation."

The alternative reading is preferable here as explained by Rawlinson:

"Because the hand of Amalek was against the throne of the Lord ... `Because' `in attacking Israel, Amalek had, as it were, lifted up his hand against God on His throne; therefore should there be war against Amalek from generation to generations."[26]

Some Bible students have trouble with the idea that God would, without mercy, blot a whole people out of existence, but this should be understood in the light of what those peoples had become. Again and again, God has destroyed whole nations, cities, or even the whole world in the case of the Flood, because it had become absolutely necessary for the continuity on earth of the knowledge and worship of God.

Was this threat against Amalek fulfilled? Indeed, yes. Centuries later, during the reign of King Saul, God sent that monarch with a commission to destroy utterly the Amalekites, but Saul did not obey, because of which disobedience he was rejected as King of Israel. He saved King Agag alive, and presumably some of the king's posterity. That it would have been far better for Saul to have obeyed is seen in the fact that in later generations, Haman the Agagite (Esther 3:1) actually plotted and very nearly carried out the murder of the whole Jewish race. God never ordered the destruction of any man or any people except upon the holy principle of what was necessary for the fulfillment of the purpose of God for the redemption of mankind.