Isaiah 41:23

הַגִּידוּ הָאֹתִיּוֹת לְאָחוֹר וְנֵדְעָה כִּי אֱלֹהִים אַתֶּם אַף־תֵּיטִיבוּ וְתָרֵעוּ וְנִשְׁתָּעָה ונר֯א יַחְדָּו׃

Qere: וְנִרְאֶה

23 Declare the things that are to come after, so we may know that you are gods. And more, do some good or do some evil, so that we will be dismayed and terrified together.

הַגִּידוּ הָאֹתִיּוֹת לְאָחוֹר Declare the things that are to come after,  הַגִּידוּ hifil imperative (m. pl.). The hifil is often causative, and this is a good example. The root נָגַד means "be known" or "be conspicuous," and in the hifil means to make something known or conspicuous. הָאֹתִיּוֹת is a qal participle of אָתָה, "come," which is pinch-hitting here for the more common בּוֹא. Isaiah seems to like the word אָתָה, whcih also occurs in Aramaic. It is rare elsewhere (Jer. 3:22). We wouldn't expect הָאֹתִיּוֹת "the coming things" to be in the construct state here, but note that the word is connected closely to לְאָחוֹר "to the back part (afterward)" by munah.

וְנֵדְעָה כִּי אֱלֹהִים אַתֶּם  so we may know that you are gods.  וְנֵדְעָה is a qal cohortative, expressing purpose. Here אֱלֹהִים is genuinely plural, spoken in derision and holy sarcasm. An Mp note says that the form וְנֵדְעָה occurs six times (cf. comments on 41:22). Another note counts only two occurences of the phrase אֱלֹהִים אַתֶּם "you are gods" (Psalm 82:6).

אַף־תֵּיטִיבוּ וְתָרֵעוּ And more, do some good or do some evil,  The conjunction אַף can mean the same thing as a conjunctive waw, but it can also resemble the ascensive καί in Greek. Here the ascensive or building idea seems right. תֵּיטִיבוּ is the hifil imperfect (יטב) carrying the same cohortative sense as the previous verbs. The same is true of the hifil imperfect וְתָרֵעוּ, "do evil."

וְנִשְׁתָּעָה וְנִרְאֶה יַחְדָּו so that we will be dismayed and terrified together. The qere ונרא lacks only the cohortative heh ending. The ketib does not end with the qal cohortative form, however. The Mp note continues to tell us that this is one of four times the word is written this way (Gen 37:20; 2 Kings 7:13; Isaiah 41:23 and 66:5), and one time it is written as a waw-consecutive imperfect (1 Sam 10:14). יַחְדָּו is an adverb, "together" from the root יַחַד. Here is a fairly typical case of older forms which add letters at the end of the word, more often in poetry.

We haven't heard the last from וְנִרְאֶה. The BHS apparatus says that if we read with the ketiv, then the root would be ,ירא "fear." But if we read with the qere, then the root would likely be רעה, "see." Neither reading changes the overall meaning of the text. Remember that the qere/ketiv system was simply the Masorete's way of recording textual variants about which he was aware. He couldn't alter the text, but if he knew about a different reading of a passage or had one before him, he could put it into the margin.