If God is already King, what is the prayer waiting for?
The next line says Hashem is King, was King, and will be King. So God's rule is not in doubt. Yet the first line looks ahead to a day when Zion is told, 'Your God has become King.' What is new on that day?
The words come from Yeshayahu, where a messenger on the mountains brings good news. The Radak (Rabbi David Kimchi, a Bible commentator in Provence, around 1200) says what changes: until that time it is not seen that He is King, but then everyone will say so.
Read that way, the prayer does not say God lacks power now. It says the world cannot see it yet, and it opens with eyes. In the next verse in Yeshayahu, the watchmen will see it 'eye to eye' when Hashem returns to Zion. Ibn Ezra (a Spanish commentator of the 1100s) reads that plainly: they will all see it with their own eyes. The Radak reads it as a vision of prophecy, which he says stopped with the last prophets and will return at the time of salvation.
The ending leans the same way. 'Will always reign over us' can sound like a request. The Mishnah Berurah (a central commentary on daily Jewish law, written around 1900) says to mean it as praise, that God will reign forever, and not as a request to bring the redemption closer, since a blessing's closing words carry no request.
Abudarham reads the word 'always' as hope too: from the days of the Mashiach on, no more exile. The sources do not ask you to choose between praise and hope. Both fit the same words.
Yeshayahu 52:7-8,Radak on Yeshayahu 52:7-8,Ibn Ezra on Yeshayahu 52:8,Mishnah Berurah 236:15,Abudarham, Weekday Evening ServiceIs this a real blessing if it has no 'Blessed' at the start and some people skip it?
Most blessings open with 'Blessed are You, Hashem.' This one does not. The Tur (a law code from the 1300s) says that two other blessings around the Shema, Ahavat Olam and Emet Ve'emunah, also skip that opening, because each is joined to the one next to it. Abudarham says Yiru Eineinu is joined in the same way to Hashkiveinu (the blessing asking God to let us lie down in peace), since the verses in between are not a break.
It does end with 'Blessed are You, Hashem.' The Tosafot say that when the rabbis set up the verses before it, they set up this closing blessing along with them.
Was everyone expected to say it? The Tur writes that some of the great rabbis had the custom not to say these verses and Yiru Eineinu. The Baruch Hashem L'olam page tells who they were and why.
Someone who skipped it may want to say it after the Amidah. For that case the Mishnah Berurah advises stopping at 'we have no king except You' and leaving off the closing blessing. He admits that a blessing without its closing does not count as a blessing at all. But since even before the Amidah this is only a custom, he says, do not add to it.
So it has the form of a blessing and the weight of a custom.
Tur, Orach Chaim 236,Abudarham, Weekday Evening Service,Tosafot on Berakhot 4b,Mishnah Berurah 236:11If Maariv is optional, why does it matter what comes right before it?
Maariv is the evening prayer. The Gemara (the main record of the rabbis' discussions) says in Berakhot 4b that Rabbi Yochanan taught: who has a place in the World to Come? One who connects the redemption blessing, the one right after the evening Shema, to the evening prayer, with nothing in between.
At night Hashkiveinu sits in between. The Gemara answers that since the rabbis set it up, it counts as a long version of the redemption blessing. (The Hashkiveinu page explains why.)
The same page mentions a view that the evening prayer is only optional, and argues against it. But the Tosafot write that the law follows that view, and they raise the puzzle themselves: we rule that it is optional, yet we also follow Rabbi Yochanan. Their answer is that even if Rabbi Yochanan agrees it is optional, he still requires the connection.
Now to our prayer. The Machzor Vitry says the heads of the yeshivot added this closing blessing because the evening prayer is optional: to announce that you do not have to connect redemption to prayer. The Tosafot report a similar idea from Seder Rav Amram, an early prayer book: the Kaddish said before the Amidah shows there is no need to connect. They reject it: 'This does not seem right,' since Rabbi Yochanan holds the evening prayer is required, and the law follows him. So, they say, it is right to be strict and not talk in between.
That is how the Shulchan Aruch rules: even those who say the verses and Yiru Eineinu should not pause between Yiru Eineinu and the Amidah.
Berakhot 4b,Tosafot on Berakhot 4b,Machzor Vitry, Order of Maariv 101,Shulchan Aruch, Orach Chaim 236:2