(12) When you have set aside in full the tenth part of your yield—in the third year, the year of the tithe—and have given it to the Levite, the stranger, the orphan, and the widow, that they may eat their fill in your settlements, (13) you shall declare before Adonai your God: “I have cleared out the consecrated portion from the house; and I have given it to the Levite, the stranger, the fatherless, and the widow, just as You commanded me; I have neither transgressed nor neglected any of Your commandments: (14) I have not eaten of it while in mourning, I have not cleared out any of it while I was unclean, and I have not deposited any of it with the dead. I have obeyed Adonai my God; I have done just as You commanded me. (15) Look down from Your holy abode, from heaven, and bless Your people Israel and the soil You have given us, a land flowing with milk and honey, as You swore to our fathers.”
We have done what you decreed for us: do that which You must do (Rashi). The word used by Rashi for "decree," gezeirah, generally implies a harsh command, and how does that fit into this context? If we examine it, though, we will realize that this is indeed a harsh decree. After all, how can a Jew be commanded to say: "I have done all that You commanded me"? Can any person make such a declaration without lying? Thus the decree is that we must make such a declaration regardless of the fact that it is not true.
R. Menahem Mendl of Kotzk
And have give it to the Levite, the stranger, the oprhan, and the widow, that they may eat within your gates, and be filled... The Torah added the word "and be filled" to teach us that when one gives tzedakah, they must be generous in how much they give.
Tiferet Shlomo
(ד) עַל הַסֵּדֶר הַזֶּה מַפְרִישִׁין בְּשָׁנָה רִאשׁוֹנָה מִן הַשָּׁבוּעַ וּבַשְּׁנִיָּה וּבָרְבִיעִית וּבַחֲמִישִׁית. אֲבָל בַּשְּׁלִישִׁית וּבַשִּׁשִּׁית מִן הַשָּׁבוּעַ אַחַר שֶׁמַּפְרִישִׁים מַעֲשֵׂר רִאשׁוֹן מַפְרִישׁ מִן הַשְּׁאָר מַעֲשֵׂר אַחֵר וְנוֹתְנוֹ לָעֲנִיִּים וְהוּא הַנִּקְרָא מַעֲשַׂר עָנִי. וְאֵין בִּשְׁתֵּי שָׁנִים אֵלּוּ מַעֲשֵׂר שֵׁנִי אֶלָּא מַעֲשַׂר עָנִי. וְעָלָיו נֶאֱמַר (דברים יד כח) "מִקְצֵה שָׁלֹשׁ שָׁנִים תּוֹצִיא אֶת כָּל מַעְשַׂר תְּבוּאָתְךָ בַּשָּׁנָה הַהִיא וְהִנַּחְתָּ בִּשְׁעָרֶיךָ" (דברים יד כט) "וּבָא הַלֵּוִי". וְעָלָיו נֶאֱמַר (דברים כו יב) "כִּי תְכַלֶּה לַעְשֵׂר":
(4) According to this system, they should tithe, in a seven year cycle, the first, second, fourth, and fifth years, but on the third and the sixth years of the seven year cycle, after one has tithed ma'asér rishon, one should take out from the remainder another tithe [one-tenth] and give it to the poor. This is called ma'esar ani. In these two years there is no ma'asér sheni but instead ma'esar ani.118See Babylonian Talmud Rosh Hashanah 12b. About this it is written, (Deut. 14:28-29) Every third year you shall bring out the full tithe of your yield of that year, but leave it within your settlements. Then the Levite, [who has no hereditary portion as you have, and the stranger, the fatherless, and the widow in your settlements shall come and eat their fill, so that the LORD your God may bless you in all the enterprises you undertake.] And about this it is written, (Deut. 26:12) When you have set aside in full the tenth part [of your yield in the third year--the year of the tithe--and have given it to the Levite, the stranger, the fatherless, and the widow, that they may eat their fill in your settlements].