Maaser Sheni, Chapter Five, Mishnah Eleven
This mishnah continues to expound up Deuteronomy 26.
1) According to all Your commandments which You have commanded me, thus, if he took out maaser sheni before the first tithe he cannot make the confession.
2) I have not transgressed any of Your commandmentsI have not set apart [tithes] from one kind for a different kind, nor from plucked [produce] for [produce still] joined [to the soil], nor from new [produce] for old [produce], nor from old [produce] for new.
3) Neither have I forgotten I have not forgotten to bless You, nor to make mention of You name over it.
Section one: The confessor states that he has properly performed all of the mitzvot involved with separating tithes. The first issue is that he has performed the tithes in their proper order. He didnt take out maaser sheni before he took out first tithe (see Terumot 3:6).
Section two: He now confesses that he didnt do anything else that is prohibited when it comes to tithing. We have learned all of these issues before (see Terumot 1:5, 2:4). Basically, one has to give terumot and maasrot from like produce, and one cant separate one type of produce in order to exempt another.
Section three: When one separates terumah and tithes, one must make a blessing, Who has sanctified us with His commandments and commanded us to separate terumot and maasrot. I have not forgotten is a reference to the fact that he didnt forget to recite this blessing.