Exode 17:16

And he said, Because the Word of the Lord hath sworn by the throne of His glory, that He by His Word will fight against those of the house of Amalek, and destroy them unto three generations; from the generation of this world, from the generation of the Meshiha, and from the generation of the world to come.

FOR THE HAND UPON ‘KEIS Y-AH’ (THE THRONE OF THE ETERNAL). “The hand of the Holy One, blessed be He, is raised to swear by His throne that He will maintain [a state of] war and enmity against Amalek forever. Now what is the significance of the word keis, and why does it not say kisei [as usual]? Furthermore, even the Divine Name is divided into half! [The answer is that] the Holy One, blessed be He, swore that the throne will not be perfect and the Name will not be full until He will blot out the name of Amalek the son of Esau. And when his name will be blotted out, then will G-d’s Name be full and the throne perfect, as it is said, The foe — they are destroyed; perpetual ruins. [This refers to Esau, of whom it is said, And he kept his wrath for ever.] Their very memorial is perished. What is written after that? And the Eternal is enthroned for ever. Thus you see [that after Amalek’s memory has perished], G-d’s Name is full. He hath established ‘kis’o’ (His throne) for judgment. Thus you see that the throne will be perfect.” Thus far the language of Rashi, and it is a Midrash of the Sages. 11.
Some scholars explain the verse as meaning that “when there will be a ‘hand,’ [i.e., king, as explained further], upon the throne of the Eternal, the Eternal will have war with Amalek, and so shall it be from generation to generation.” The purport of this is that when there will be a king in Israel sitting upon the throne of the Eternal, he shall wage war against Amalek, thus alluding to Saul, the first king [of Israel]. And so shall it continue from generation to generation, that every king of Israel shall be duty-bound to fight with them until their name will extinct.
The following is also a Midrash of the Gemara,, Note 204. as found in [Tractate Sanhedrin] in the chapter of the High Priest: “By saying, The hand upon the throne of the Eternal: the Eternal will have war with Amalek from generation to generation, Scripture intimates that the Israelites must first appoint a king over themselves [before they are to annihilate the offspring of Amalek], for the throne of the Eternal refers only to the king, as it is said, Then Solomon sat on the throne of the Eternal. In line with the plain meaning of Scripture, this is correct.
And by way of the Truth, [that is, the mystic lore of the Cabala, the verse is to be understood as meaning] that the Hand, [i.e., the attribute of justice], which is upon the throne of Y-ah, and which is the war from the Eternal, will continue with Amalek from generation to generation, for the high attribute of justice will pursue his extinction forever from generation to generation. The Midrash of the Sages [mentioned above] concerning “the full Divine Name” and “the perfect throne” allude to this [interpretation by way of the Truth].
Now the reason for the punishment of Amalek, i.e., why punitive measures were meted out to him more than to all other nations, is that when all the nations heard [of G-d’s visitation upon the Egyptians], they trembled. Philistia, Edom, and Moab and the inhabitants of Canaan melted away from before the terror of the Eternal, and from the Glory of His majesty, whereas Amalek came from afar as if to make himself master over G-d. It is for this reason that it is said concerning him, and he feared not G-d. Besides, he was a descendant of Esau and related to us, a passer-by who meddles with a quarrel not his own.
Yithro

HE SAID, “IT MEANS, ‘HAND UPON THE THRONE OF THE LORD!’ ETC. That is why I name the altar "Adonai Nisi," like the name of a person called Eliezer [God is my help] or Imanu'el [God is with us], for God has lifted His hand on His throne that He has a war against Amalek through the generations, in the manner of (Isa. 32:40), "I raise My hand to heaven." This is the essential plain meaning. And some interpret it: "When My hand and strength will be on Yah's throne, which is the throne of the kings of Israel, then there will be a war against Amalek. But this does not seem to me correct at all, for [if so,] it should have said, "When there will be [ki tihyeh] a hand." However, this refers above, as I have explained, and its meaning is "Hereby [harei] hand on the throne of Yah."

ויאמר כי יד על כס י-ה, Moses explains the reason and purpose of his prayer being the fact that G’d Himself had sworn an oath to remain at war with Amalek from generation to generation. If G’d is at war with that nation, we as G’d’s representative on earth, must certainly also be at war with that nation. It is what our sages referred to when they said that three commandments cannot be fulfilled until the Jewish people are securely settled in the land of Israel, 1) appointment of a king; 2) destroying the last vestiges of Amalek; 3) the building of a permanent Temple. Moses therefore had prayed for the time when these three hallmarks of Jewish history could be attained. (Sanhedrin 20)

ויאמר כי יד על כס י-ה, he (Moses) said: “as soon as G–d’s hand on His throne will become firmly established throughout His universe, He will go to war against Amalek. The word יד describing an active monarchy is found in Samuel I 15,12,. I have heard in the name of Rabbi Aaron Halevi of blessed memory who questioned that the subject of the word יד here is Amalek, seeing that it says: ”I will surely wipe out.” How could Amalek have said this of himself? On the other hand in Deuteronomy 25,19, Moses commands the people in the name of the Lord that once the time has come when there is no more antisemitism, instead of letting bygones be bygones, the Jewish people are charged with seeing to it that even the mention of the name Amalek will be eradicated once and for all. Personally, I do not see a problem there at all. In our portion we discuss times when Amalek raises its hand against Israel. At such a time we need G–d to defend us against him. In Deuteronomy, it is presumed Amalek is raising his sword against the Temple, G–d’s home on earth. When the residence of the Lord is in danger, it is G–d’s people, we, who have to rise up in its defense. Jerusalem is called the throne of G–d. His throne is not secure as long as there is still any descendant of Amalek alive on this earth. We read in Psalms 9,8: וה' לעולם ישב כונן למשפט כסאו, “but the Lord abides forever; He has set up His throne for judgment.” This is the reason why the dead are unable to praise the Lord (Psalms 115,17) seeing that being dead they cannot battle Amalek. This is why David continues in Psalm 118 with: לא אמות כי אחיה ואספר מעשי ה' וגו', “I do not wish to die, as I want to be able to tell of the great deeds of the Lord, etc.”