Hilchos Maaser Sheini and Neta Revai 11:12

We know that one may not recite the tithe confession until he gets rid of the agricultural gifts because Deut. 26:13 says, “I have removed all the holy things from the house.” “Holy things” means second tithe and neta revai, which the Torah refers to as holy. “From the house” means challah, which is a gift given to kohanim from one’s home (rather than from one’s field). “I gave it to the Levi” means first tithe (which is given to a Levi). “I also gave it” means terumah gedolah and terumas maaser (which are given to a kohein). “To the convert, the orphan and the widow” means the tithe for the needy, plus leket, shich’cha and peah. These last three are included in the tithe confession but failure to leave these gifts doesn’t keep one from reciting it.

Hilchos Maaser Sheini and Neta Revai 11:13

The gifts must be separated in their assigned order, after which one recites the tithe confession. This is because the Torah continues, “according to all Your commandments that You commanded me.” Accordingly, if someone gave second tithe before first tithe, he may not recite the tithe confession. If someone’s untithed produce was burned, he may not recite the tithe confession because he didn’t separate the agricultural gifts or give them to the requisite recipients. When first tithe was given to kohanim (which was in the time of Ezra), the tithe confession wasn’t recited because of the phrase “I gave it to the Levi.”