Isaiah 40:25

וְאֶל־מִי תְדַמְּיוּנִי וְאֶשְׁוֶה יֹאמַר קָדוֹשׁ׃

25 To whom will you compare me? Would I be like him? says the Holy One.

This verse repeats the thought of 40:18, "like a refrain" (Pieper).

וְאֶל־מִי תְדַמְּיוּנִי To whom will you compare me? תְדַמְּיוּנִי is a piel imperfect (2 masc. plural with 1 sg suffix) from דָּמָה, "be like," which in the intensive piel means "compare." In this verb, the yod returns irregularly in the piel taking over for the root's final radical. The Mp note tells us that this form occurs twice (Isaiah 40:25 and 46:5). The other Mp note in this line for the phrase וְאֶל־מִי was covered in verse 18 of this chapter.

וְאֶשְׁוֶה יֹאמַר קָדוֹשׁ Would I be like him? says the Holy One. Atnach separates וְאֶשְׁוֶה from the rest of the verse; it might seem like an unusual break, but it's typical for the Masoretes to separate "says the Lord" and its variations from the rest of a verse in this way. וְאֶשְׁוֶה is a qal cohortative (not a waw-consecutive imperfect) with the Lord asking a rhetorical question. The verb is שָׁוָה, a doubly-weak verb which here retains all of its radicals. There is no direct object to this verb of comparison but it's evident from the parallelism that it is implied.

"Holy One" is simply the adjectival קָדוֹשׁ without any modifier except the one implied in "says" (יֹאמַר). Holiness is what sets God apart from me and from the rest of his creation. We are all subject to the Fall; God is not. When Satan fell, he dragged some of the angels with him. When Adam and Eve fell, they dragged down all of mankind and the created universe, too. Adam's sin affects me, my wife and our children as well as the weeds in our yard, the moon overhead, the sparrows making their nest in our birdhouse, and the gravel the street. None of it; none of us is holy because of the Fall. The Fall brought us all down. But God's קָדוֹשׁ, his holiness, is what he now gives to us through Christ, not because we deserve it, but because God loves us and wants to give his קָדוֹשׁ to us once again. Isaiah may have said this all before, but the reason it makes a good refrain is that it's worth saying again and again: God is קָדוֹשׁ (kadosh), God is holy. And he covers us with Christ's holiness to make us his own.