Charles Ellicott Commentary Exodus 17:16

"And he said, Jehovah hath sworn: Jehovah will have war with Amalek from generation to generation." — Exodus 17:16 (ASV)

Because the Lord has sworn that the Lord will be at war with Amalek.— Heb., because (his) hand is against the throne of Jehovah, (there shall be) war for Jehovah with Amalek, and so forth. The Hebrew can scarcely be said to be “obscure.” It gives plainly enough the sense which our translators have placed in the margin. Amalek, by attacking Israel, had lifted up his hand against the throne of God; therefore, God would wage war against him from generation to generation.