Why is so much emphasis given to the line "us'shuva us'fila utz'daka maavirin..." in the Rosh Hashana and Yom Kipur prayers? It seems to be the most emphasized line of all, with people shouting it and concentrating on the words heavily, with the machzorim (prayer books) emphasizing it with large letters set by themselves in the middle of a line. I mean, it's just a statement of fact, not a viduy (admission of sin) or declaration of malchus shamayim or plea. Why is there so much stress on this statement of fact?
I believe it's to encourage people to actually do it.
That's the simplest take-home lesson from the Davening.
This is more of an extended comment....
There are a lot of things in here that are relevant to the season. One thing is that the next posuk is:
עַתָּה, עֵינַי יִהְיוּ פְתֻחוֹת, וְאָזְנַי, קַשֻּׁבוֹת--לִתְפִלַּת, הַמָּקוֹם הַזֶּה.
Now Mine eyes shall be open, and Mine ears attent, unto the prayer that is made in this place.
We might be petitioning G-d by reminding G-d of the promise of forgiveness that G-d made to Shlomo.
Alternatively, we might be telling ourselves the first half of that promise - that G-d is all-powerful:
הֵן אֶעֱצֹר הַשָּׁמַיִם וְלֹא-יִהְיֶה מָטָר, וְהֵן-אֲצַוֶּה עַל-חָגָב לֶאֱכוֹל הָאָרֶץ; וְאִם-אֲשַׁלַּח דֶּבֶר, בְּעַמִּי.
If I shut up heaven that there be no rain, or if I command the locust to devour the land, or if I send pestilence among My people;
It's also reasonable to think that it is referring to the prayer Shlomo made to G-d in the perek beforehand, notably v.21:
וְשָׁמַעְתָּ אֶל-תַּחֲנוּנֵי עַבְדְּךָ, וְעַמְּךָ יִשְׂרָאֵל, אֲשֶׁר יִתְפַּלְלוּ, אֶל-הַמָּקוֹם הַזֶּה; וְאַתָּה תִּשְׁמַע מִמְּקוֹם שִׁבְתְּךָ, מִן-הַשָּׁמַיִם--וְשָׁמַעְתָּ, וְסָלָחְתָּ.
And hearken Thou to the supplications of Thy servant, and of Thy people Israel, when they shall pray toward this place; yea, hear Thou from Thy dwelling-place, even from heaven; and when Thou hearest, forgive.
כִּי יֶחֶטְאוּ-לָךְ, כִּי אֵין אָדָם אֲשֶׁר לֹא-יֶחֱטָא, וְאָנַפְתָּ בָם, ... וְהֵשִׁיבוּ, אֶל-לְבָבָם, בָּאָרֶץ, אֲשֶׁר נִשְׁבּוּ-שָׁם; וְשָׁבוּ וְהִתְחַנְּנוּ אֵלֶיךָ, בְּאֶרֶץ שִׁבְיָם לֵאמֹר, חָטָאנוּ הֶעֱוִינוּ, וְרָשָׁעְנוּ. ...שָׁמַעְתָּ מִן-הַשָּׁמַיִם מִמְּכוֹן שִׁבְתְּךָ, אֶת-תְּפִלָּתָם וְאֶת-תְּחִנֹּתֵיהֶם, וְעָשִׂיתָ, מִשְׁפָּטָם; וְסָלַחְתָּ לְעַמְּךָ, אֲשֶׁר חָטְאוּ-לָךְ.
If they sin against Thee--for there is no man that sinneth not--and Thou be angry with them, ... yet if they shall bethink themselves in the land whither they are carried captive, and turn, and make supplication unto Thee in the land of their captivity, saying: We have sinned, we have done iniquitously, and have dealt wickedly; ... then hear Thou from heaven, even from Thy dwelling-place, their prayer and their supplications, and maintain their cause; and forgive Thy people who have sinned against Thee.