It says God is King now. Then it says God will be King someday. Which is it?
Two lines sit back to back. The first says Hashem is King, was King and will be King. The second, from the prophet Zecharyah, says: "Hashem will be King over all the earth. On that day Hashem will be one and His name one." Will be King? Will be one?
The Gemara (the rabbis' discussions built on the Mishnah) asks exactly that: "Is He not one now?"
The commentators give the plain meaning. Rashi (the classic commentator, France, died 1105): all the nations will leave their empty gods and admit that He is one, and His name will be on everyone's lips. Radak (Rabbi David Kimchi, Provence, around 1200) adds that no other god will be named anywhere in the world. On this reading nothing about God changes. What changes is who knows it. The Kaddish DeRabbanan prayer has more on this verse.
The Gemara's own first answer is about how life feels. Rabbi Acha bar Chanina says this world is not like the world to come. Now, on good news we say one blessing, "who is good and does good," and on bad news a different one, "the true Judge." In the world to come there will be only the first.
Its second answer, from Rav Nachman bar Yitzchak, is about the name. Today God's name is written one way, with the letters yud and heh, and read another way, with alef and dalet. In the world to come it will be read the way it is written. You have been doing this all morning: your eyes see one name and your mouth says another.
So the two lines do not contradict each other. The first says what is true. The second says what cannot be seen yet: not everyone knows it, bad news still gets its own blessing, and even the name is not said the way it is spelled.
Zecharyah 14:9,Pesachim 50a,Rashi and Radak on Zecharyah 14:9God is King whether I say so or not. So what does saying it do?
It is a fair point. God did not become King this morning because you said so.
The Mekhilta (an early Midrash on Shemot) still treats the wording as something that matters. On the line "Hashem will be King forever and ever" in the Song at the Sea, Rabbi Yose HaGelili says: if Israel had said at the sea "Hashem is King forever," no nation would ever have ruled over them. But they said "Hashem will be King," in the future. The line in your siddur puts the present first, and Abudarham explains why: first make Him King over the present, today.
Another Midrash, Shemot Rabbah, goes further. Tehillim 93, the psalm that gives us "Hashem was King," goes on to say that God's throne stands firm "from then." The Midrash ties that word to the Song at the Sea, which opens with "then." Rabbi Berechyah says in the name of Rabbi Abbahu: "Even though You have always existed, Your throne was not settled and You were not known in Your world until Your children sang."
He compares it to a king who wins a war. His people tell him: before the war you were a king, now we have made you emperor. God was the same before the sea and after it. What settled was His throne in the world.
Pirkei DeRabbi Eliezer (a Midrash that retells the Torah starting from creation) pictures the Torah speaking to God before the world was made: "If a king has no army and no camp, over what does he rule? If no people praises the king, where is the king's honor?"
And the Gemara, explaining the Rosh Hashanah prayers, has God say: "Say verses of kingship before Me, so that you make Me King over you."
None of these sources says God is missing anything. What they describe is a kingship that is known in the world only where people declare it. The Gemara's own words for where that happens are "over you."
Mekhilta DeRabbi Yishmael on Shemot 15:18,Abudarham, Weekday Evening Service,Shemot Rabbah 23:1,Tehillim 93:1-2,Pirkei DeRabbi Eliezer 3,Rosh Hashanah 34bThe nations will sing because God judges them? Since when is that good news?
The middle verse of Tehillim 67 says: "Nations will be glad and sing for joy, because You will judge peoples fairly." Most people do not sing on the way to court.
Rashi (the classic commentator, France, died 1105) answers in one word. He reads "fairly" as judging them toward a good verdict.
Others say a fair trial is the good news in itself. Metzudat David (a commentary from the 1700s): they will be glad when they see that each one is judged as he deserves. Ibn Ezra (Rabbi Avraham ibn Ezra, Spain, 1100s), on the refrain that follows, says the peoples will thank God for His judgments too: He clears the innocent, convicts the guilty, and the earth becomes quiet.
Radak (Rabbi David Kimchi, Provence, around 1200) reads the whole psalm as being about the future, when the exiles of Jerusalem are gathered in. That fits where it sits in the siddur, right after "gather us from the nations." The peoples who come with Gog, the enemy in the prophet Yechezkel's last war, will be judged fairly, he says, and then the rest of the nations will be glad.
Midrash Tehillim (a collection of rabbinic teachings on Tehillim) names the worry behind the question. When God saves Israel, might the nations say He is playing favorites? Its answer is the psalm's refrain. No: they thank Him, "all of them." The same Midrash says God does not save Israel because of what they have done, but to make His strength and His name known.
So the sources give more than one picture: a Judge who leans toward a good verdict, a Judge who gets each case right, a Judge nobody can accuse of taking sides. In none of them are the nations singing about being punished. They sing because the One in charge is fair.
Tehillim 67:5,Rashi, Radak, Ibn Ezra and Metzudat David on Tehillim 67,Midrash Tehillim 67