Exodus 17:16

ויאמר AND HE SAID — i. e. Moses said. כי יד על כס יה BECAUSE THE HAND IS UPON THE THRONE OF JAH — the hand of the Holy One, blessed be He, is raised to swear by His throne that He will have war and enmity against Amalek to all eternity. And what is the force of כס — why does it not say as usual כסא? And the Divine Name, also, is divided into half (יה is only the half of the Tetragrammaton)! The Holy One, blessed be He, swears that His Name will not be perfect nor His throne perfect until the name of Amalek be entirely blotted out. But when his name is blotted out then will His (God’s) Name be perfect and His throne perfect, as it is said, (Psalms 9:7) “The enemy is come to an end, he whose swords were for ever” — and this refers to Amalek of whom it is written, (Amos 1:11; the paragraph is a prophecy against Edom — Esau — the father of Amalek) “he kept his wrath for ever”. The verse in the Psalm continues: “and thou didst uproot enemies, their very memorial is perished”, What does it say immediately after this? (Psalms 9:8) “But the Lord (the Divine Name as given here is the Tetragrammaton) shall now remain for ever” — you see that the Name will be perfect (after Amalek is entirely rooted out as is mentioned in v. 7); “He establishes his throne (כסאו not כס) in righteousness” — so you see that His throne will then be perfect (Midrash Tanchuma, Ki Tisa 11).

וַיֹּ֗אמֶר כִּֽי־יָד֙ עַל־כֵּ֣ס יָ֔הּ*(בכתר ארם צובה היה כתוב כֵּ֣סְיָ֔הּ בתיבה אחת) מִלְחָמָ֥ה לַיהֹוָ֖ה בַּֽעֲמָלֵ֑ק מִדֹּ֖ר דֹּֽר׃ {פ}

for he said, Because the Lord has sworn by his throne that the Lord will have war with ῾Amaleq from generation to generation.