Two questions.
1. The classic question: Chazal describe the Maaser proclamation as a Viduy.
(The first such reference is in the last perek in Maaser Sheni, Mishna 10. It is so described in other Mishnayos, like in Sotah, the Gemara and all the Rishonim. Chazal's choice of that word is difficult to understand. It might mean "attestation," or "assertion," from the root הודעה, to make known. That's what it seems from the last mishna in Maaser Sheini, where it says יוֹחָנָן כֹּהֵן גָּדוֹל הֶעֱבִיר הוֹדָיוֹת הַמַּעֲשֵׂר. But it clearly is not used that way in other mishnayos and elsewhere in Chazal. It is used as Viduy, not Hoda'ah.)
In the Torah, viduy is only used regarding confession of aveiros, such as Bamidbar 5:6-7,
דבר אל בני ישראל איש או אשה כי יעשו מכל חטאת האדם למעל מעל בה' ואשמה הנפש ההוא. והתודו את חטאתם אשר עשו והשיב את אשמו בראשו וחמישתו יסף עליו ונתן לאשר אשם לו
So why did Chazal choose this term when the man is stating that he did everything he was supposed to do?
(It is true that in English, for example, "confession" is used for a public declaration of faith in religious doctrine- "a confession of faith." But there is no confession of faith by Maaser, only by Bikkurim. By Maaser it is just a statement that he did what he is obligated to do, עשיתי ככל אשר צויתני.)
(One of the many teirutzim - The Seforno says that Chazal's use of the term Viduy it is a reference to the avodah taken away from the Bechor. This is a dochek. It is also possible that unlike Viduy of sin which comes from מודה\הודאה, this Viduy comes from וודאי, certainty- you are certifying a fact, that you did everything right. But at least we can use the Seforno's question to validate the assumption that it means to admit/confess, and that is indeed how everyone does understand it.)
2. On 26:13
ואמרת לפני ה' אלהיך בערתי הקדש מן הבית וגם נתתיו ללוי ולגר ליתום ולאלמנה ככל מצותך אשר צויתני לא עברתי ממצותיך ולא שכחתי
Rashi brings the Gemara in Brachos
ולא שכחתי. מִלְּבָרֶכְךָ עַל הַפְרָשַׁת מַעַשְׂרוֹת (ברכות מ')
Is this really a din deoraysa, that you have to make a birkas hamitzvos on Hafrashas Truma? Highly unlikely. At most, you can say that מִלְּבָרֶכְךָ is a personal expression of gratitude for the gift of such a mitzva.
From an old post on the topic:
Mar'ei makomos for Birkos Hamitzvos being De'oraysa: Rashi in Ki Savo, Devarim 26:13, and in Brochos 40b, says that "lo avarti...lo shachachti....refers to the birkas hafrasha. Tosfos Yomtov in Bikkurim 5:11, says that the whole Gemora is just an asmachta and the bracha is for sure not De'oraysa. The Tzlach in Brochos 40 brings the TYT, and argues. The Satmerer in his Vayo’el Moshe here says the same thing without bringing the Tzlach. R’ Akiva Eiger in Brochos 15 agrees with the Tzlach, but points out that the Tzlach means that the chiyuv De’oraysa to be meshabei’ach for the mitzvah is after doing the mitzvah, not before. The Shai LaTorah in Ki Savo brings the Griz and R Dovid Soloveitchik that the Gemora in Brochos is mashma that it’s a normal brochoh. The Rogotchover there brings and explains a Sifri and a Yerushalmi on this matter. The Shem Mishmuel brings from his father that he saw a Teshuvas Ri Migash that the bracha Rashi is referring to is She'hechiyanu, and that is a de'oraysa.
Reb Moshe in the new Kol Rom addresses the first question and touches on the second. He says:
The Gemara in Shabbos 31a says that when a person is brought before the Beis Din shel Maalah, they ask him
מר רבא: בשעה שמכניסין אדם לדין, אומרים לו: נשאת ונתת באמונה? קבעת עתים לתורה? עסקת בפריה ורביה? צפית לישועה? פלפלת בחכמה? הבנת דבר מתוך דבר?
Reb Moshe asks, that they ought to ask him about far more serious things, like Chillul Shabbos and treifus, or even basic mitzvos,
אם לא גזל ולמד תורה וקיים פרו ורבו והאמין בה' וכו', אלא אודות דברים שלכאורה הם מעלות נוספות.
Reb Moshe explains that this person who stands before the Beis Din is a Ben Torah and a Tzadik, who did all the mitzvos and did no aveiros. The question is whether he kept the Torah כהוגן. Not whether he stole, but whether he was careful in his finances באמונה ודקדוק מבלי להורות היתר לעצמו, whether he learned, but whether his learning was בקביעות ודבר קצוב חוק ולא יעבור. Not whether he did Pirya v'Rivya, but אם עסק בזה כהוגן.
This is what Viduy Maaser is about. Not the basic kiyum mitzvos, but kiyum with dedication and a whole heart. We see this in the words עשיתי ככל אשר צויתני; not just אשר צויתני, but ככל אשר צויתני.
This includes dinim derabanan! Of course brachos are derabanan. But a person who does mitzvos with dikduk, will make a bracha on the mitzvos. He doesn't need Chazal to be mesakein a chiyuv brachos, he will anticipate that halacha and make brachos on every mitzva because לבו אומר לו to make a bracha.
Reb Moshe continues and says that this explains the word "Viduy." His words-
לכן נקרא שפיר וידוי מעשר, דיש בזה ענין של וידוי והתעוררות על שאר מצות שאין עושין כהוגן.
Diverging from Reb Moshe's last line, I would say a different answer. I would say that since, as Reb Moshe says, this declaration is about doing mitzvos with love and passion, it is concomitant that the person feels that he did not do enough. Simply (not really simple!) doing all the mitzvos and avoiding aveiros is binary: Do, or do not do. You can get a 100% on that test. But once we're talking about love and passion, you feel that what you have done is nothing, if only you could do more!
Reb Moshe says the Viduy is for other mitzvos, which you have not done as well as Maaser. I am saying that as soon as you step over into the realm of ahavas Hashem and ahavas Yisrael, it is impossible to do enough. Yes, I even made brachos on hafrasha. Yes, I did it with tuv leiv. Yes, I sought out and delivered it to the people who needed it. But I didn't do it as well as I should have.
That is the Viduy. Mitzvos, done properly, are done with a driving urge to show your love for the Ribono shel Olam and His Torah. As we say in ידיד נפש, we are so love-sick that we are consumed with a desire to do more.
- הָדוּר נָאֶה זִיו הָעוֹלָם
- נַפְשִׁי חוֹלַת אַהֲבָתֶךָ.
- אָנָּא אֵל, נָא, רְפָא נָא לָהּ
- בְּהַרְאוֹת לָהּ נֹעַם זִיוֶךָ,
- אָז תִּתְחַזֵּק וְתִתְרַפֵּא,
- וְהָיְתָה לָהּ שִׂמְחַת עוֹלָם.
That is the Viduy of Maaser. I have done everything, and it's not nearly good enough.
We are beginning the season of Selichos, and the highlight of Selichos is the Viduy. You should know, and it really matters now, that there are two kinds of Viduy. There is the Viduy of Yamim Noraim, of Yir'ah, of what you did wrong; and there is the viduy of Bikkurim, of Ahavah, that I wish I could have done more. It wouldn't hurt to have a little Bikkurim Viduy in the Yamim Noraim.