Maaser Sheni, Chapter 5, Mishnah 12. This mishnah continues the preceding mishnayos, which elaborate on the text of the confession of the tithes that a person recites at the time of the biur (removal).
"Lo achalti be'oni mimenu":
In the wording of the confession a person states that he did not eat from the maaser while he was in a state of aninus. An onen is someone who has lost one of the relatives for whom he must sit shivah, and his status is divided into two categories:
Aninus from the Torah: on the day of the death itself, even after the burial.
Aninus by rabbinic law: the night following the day of the death, as well as the day of the burial when it is not the day of the death.
What is derived here relates specifically to maaser sheni, which an onen is forbidden to eat. Since a person declares in the confession "lo achalti" - I did not eat - it follows that if he did eat from it while in a state of aninus, he can no longer recite the confession, for he has violated what is stated in it.
"Velo bi'arti mimenu betamei":
The mishnah teaches that if a person separated the maaser sheni while he was in a state of tumah, he cannot recite the confession. The commentators find this derivation difficult to understand: how do we extract from the words "asher lo bi'arti" both that a person may not eat maaser sheni while he is tamei, and also that he may not separate maaser sheni while he is tamei? This question is discussed at length in the words of the commentators.
"Velo natati mimenu lemeis":
What does this mean? The mishnah explains that it refers to two matters:
A coffin and shrouds: "I did not purchase with them" - with maaser sheni money - a coffin or shrouds for the deceased.
Giving to onenim: I did not give it to other people who are in a state of aninus, who have just lost a family member. This too is included in the prohibition of giving it "to the dead."
Here too the commentators raise a difficulty: why is it necessary to exclude using maaser sheni money for a coffin or shrouds, when in general maaser sheni money may only be used for food needs? Some have suggested that when a person uses maaser sheni money for things that are not fit for eating, he always has the option of taking other money afterward, exchanging it, and eating it as maaser sheni, and this might still allow him to recite the confession; but if he used it for objects that are not fit for eating, that prevents him from reciting the confession. This is one possible resolution.
"Shamati bekol Hashem Elokai" and "asiti kechol asher tzivisani":
The continuation of the text of the confession: "Shamati bekol Hashem Elokai" - I listened to the voice of Hashem my God - meaning that I brought it to the Beis HaMikdash. "Asiti kechol asher tzivisani" - I did according to all that You commanded me - the mishnah understands this to mean that I rejoiced in it, and that I also gladdened other people through the maaser sheni.
In summary: This mishnah explains the details of the wording of the confession of the tithes - "lo achalti be'oni" (the prohibition of eating maaser sheni in a state of aninus, and the laws of an onen from the Torah and by rabbinic law), "velo bi'arti mimenu betamei" (separating and eating in a state of tumah), "velo natati mimenu lemeis" (a coffin and shrouds, and giving to onenim), and alongside them the positive declarations: "shamati bekol Hashem Elokai" - bringing it to the Beis HaMikdash, and "asiti kechol asher tzivisani" - rejoicing in it and gladdening others through it. We also noted the difficulties raised by the commentators regarding these derivations and one of the resolutions offered.