Rav Joseph B. Soloveitchik, Worship of the Heart: Essays on Jewish Prayer (Jersey City: 2003), Shalom Carmy, ed., 147-148
The act (ma'aseh) of prayer is formal, the recitation of a known, set text; but the fulfillment of prayer, its kiyyum, is subjective: It is the service of the heart. The intention (kavvanah) required for prayer is not like the kavvanah required for other mitzvot. In other commandments the intention is not the most important element. It is a secondary element, even if it is required for fulfillment of the mitzvah. Rather it is the act, the concrete action, that is primary, and kavannah simply accompanies the action. With prayer, however, kavvanah is the essence and substance: prayer without intention is nothing.
(יג) רַבִּי שִׁמְעוֹן אוֹמֵר, הֱוֵי זָהִיר בִּקְרִיאַת שְׁמַע וּבַתְּפִלָּה. וּכְשֶׁאַתָּה מִתְפַּלֵּל, אַל תַּעַשׂ תְּפִלָּתְךָ קֶבַע, אֶלָּא רַחֲמִים וְתַחֲנוּנִים לִפְנֵי הַמָּקוֹם בָּרוּךְ הוּא, שֶׁנֶּאֱמַר (יואל ב) כִּי חַנּוּן וְרַחוּם הוּא אֶרֶךְ אַפַּיִם וְרַב חֶסֶד וְנִחָם עַל הָרָעָה. וְאַל תְּהִי רָשָׁע בִּפְנֵי עַצְמְךָ:
(13) Rabbi Shimon says: Be careful in the reciting of Shema (and praying). When you pray, do not make your prayer fixed, rather prayers for mercy and supplication before the Omnipresent Blessed One, as it says (Joel 2, 13), "For ha-Shem is gracious and merciful, long-suffering and full of kindness, and repents of the evil." And do not be wicked in your own eyes.
(ה) לְהִתְפַּלַּל לוֹ, שֶׁנֶּאֱמָר: "וַעֲבַדְתֶּם, אֵת ה' אֱלֹהֵיכֶם" (שמות כג, כה) – עֲבוֹדָה זוֹ תְּפִלָּה.
(5) To pray to him, as it is stated, "And ye shall serve the LORD thy God" (Deuteronomy 23:25), service [meaning] prayer.
תני: ר' יוסי אומר, "כל המשנה על המטבע שטבעו חכמים לא יצא ידי חובתו."...
ר' מאיר אומר, "אפילו אמר 'ברוך שברא החפץ הזה מה נאה הוא', זה יצא." ר' יעקב בר אחא בשם שמואל, "הלכה כר' מאיר."
מילתיה דרב אמרה כן. חד פרסוי אתא לגבי רב בגין, "דאנא אכל פיסתי ולא אנא חכים מברכא עליה ואנא אמר 'ברוך דברא הדין פסא'. נפיק אנא ידי חובתי?" א"ל, "אין."
It was taught: R. Yose says, “Anyone who alters the formula [for blessings] established by the sages does not fulfill his obligation.”...
R. Meir says, “Even if one said, ‘Blessed be He who created this object. How beautiful it is,’ he fulfilled his obligation” R. Jacob bar Aha in the name of Samuel, “The law accords with the view of R. Meir.”
A tradition concerning Rav supports this. A Persian once came before Rav: “I ate a loaf of bread but because I did not know which blessing to recite over it, I said, ‘Blessed be He who created the loaf of bread.’ Did I fulfill my obligation?” He said to him, “You did.”
[Translation from R. Tzvee Zahavy]
(ז) וַיִּקַּח֙ סֵ֣פֶר הַבְּרִ֔ית וַיִּקְרָ֖א בְּאָזְנֵ֣י הָעָ֑ם וַיֹּ֣אמְר֔וּ כֹּ֛ל אֲשֶׁר־דִּבֶּ֥ר ה' נַעֲשֶׂ֥ה וְנִשְׁמָֽע׃
(7) And he [Moses] took the book of the covenant, and read in the hearing of the people; and they said: ‘All that the Eternal has spoken will we do, and obey.’
תלמוד גדול או מעשה גדול נענה רבי טרפון ואמר מעשה גדול נענה ר"ע ואמר תלמוד גדול נענו כולם ואמרו תלמוד גדול שהתלמוד מביא לידי מעשה.
Is learning greater or deed greater? Rabbi Tarfon answered, deed is greater. Rabbi Eli'ezer responded and said, learning is greater. Then someone else responded to both of them and said that learning is greater, as learning leads to deed.