Menachos, Chapter Seven, Mishnah 6, the last in the chapter. In the previous Mishnah we learned that a person who is going to bring a Todah offering, and who takes upon himself an obligation to do so, must purchase it with his own private money and not with maaser sheni money. Our Mishnah comes to provide the basic source for this law. This is a derashah, and therefore the matter is not logically compelling; rather, this is the source from the midrashic angle.
The Source of the Law in the Verse:
From where do we know that a person who takes upon himself an obligation to bring a Todah must use money from his own pocket, and cannot use maaser sheni money? The starting point is the verse in Devarim (16:2): "Vezavachta pesach laHashem Elokecha tzon uvakar" - "And you shall slaughter the Pesach offering to Hashem your God, from the flock and the herd."
"Tzon" - goats and sheep.
"Bakar" - cattle.
These are in fact the only possibilities for an offering: every sacrifice comes from a cow, a goat or a sheep. But these words are completely superfluous at the end of the verse. And not only are they unnecessary, it is clear that they are not speaking about the Pesach offering itself, since the Pesach offering comes specifically from goats or sheep, as the verse says in Shemos (12:5): "From the sheep or from the goats shall you take it." If so, what are they doing here?
The Comparison to the Pesach Offering:
The Mishnah compares other obligatory offerings to the Pesach offering. This is not stated explicitly in the Mishnah at all, but this is how the Gemara explains it: just as the Pesach offering must come from a person's own private money and not from maaser sheni money, so too these. And from where do we know this? The Pesach that was brought in Egypt is the model, and at that time there was no maaser sheni at all - the Torah had not yet been given, and necessarily the Pesach was purchased with private funds. And we learned that the laws of the later Pesach offerings are derived from the Pesach of Egypt, and therefore the Pesach of each and every year is also purchased with one's personal money, from chullin.
The verse therefore teaches that animals that come as "tzon uvakar," that is, offerings which are fundamentally voluntary offerings, and which a person has taken upon himself as an obligation, have the same law as the Pesach:
Todah: a cow, a goat or a sheep.
Shelamim: a cow or a sheep.
Olah: a cow, a goat or a sheep.
From the moment a person takes upon himself to bring them and makes them an obligation, like the Pesach which is an obligation, he must pay for them out of his own pocket.
The Wording of the Mishnah:
The verse says "Vezavachta pesach laHashem Elokecha tzon uvakar", and the Mishnah says: "Vahalo ein pesach ba ela min hakevasim umin ha'izim" - the only possibilities for bringing a Pesach offering are a goat or a sheep; why then is cattle mentioned? "Im kein lamah ne'emar tzon uvakar" - if so, why does it say "from the flock and the herd"? "Ela lehakish kol haba min habakar umin hatzon lapesach" - to make a comparison and connect: every offering that comes from cattle, goats or sheep as an obligation is like the Pesach offering. And in what respect? "Mah hapesach shehu ba bechovah" - the Pesach offering never comes as a voluntary offering, but always in the context of an obligation, "eino ba ela min hachullin" - a person must pay from his own pocket in order to purchase his Pesach offering, and he cannot use maaser sheni money; "af kol davar shehu ba bechovah" - so too any offering brought in the context of an obligation, because he said "harei alai" ("it is incumbent upon me"), "lo yavo ela min hachullin" - may come only from chullin.
"Lefichach ha'omer harei alai todah" - a person who says, "I take upon myself to bring a todah offering," "harei alai shelamim" - or who takes upon himself to bring a shelamim offering, "ho'il vehem ba'im bechovah" - these are no longer voluntary offerings, for he could have donated and brought a shelamim or a todah as a free-will gift, and once he made them an obligation, "lo yavo ela min hachulin" - he must pay for them out of his own pocket.
The difference between "harei alai" and "harei zu":
This point deserves clarification: everything said here applies because he said "harei alai," meaning "I obligate myself to bring this offering." But there is no question that a person may use the wording "harei zu," which does not impose an obligation upon himself: he may take money of maaser sheni, buy with it a sheep, a goat or a cow, and say "harei zu todah" or "harei zu shelamim," and it is valid. The result is a shelamim or a todah purchased with maaser sheni money, and that is fine, because they are not brought as an obligation.
The law of the nesachim:
The final clause of the Mishnah addresses a different point. The previous Mishnah taught that a person who says, "I take upon myself a todah and its bread from maaser," has fulfilled his obligation and may bring it from maaser money. However, if he said, "I take upon myself a todah and its bread, and also the nesachim that accompany it" - for a todah, like a shelamim, has nesachim, the wine libation and the meal offering that comes with it - and he said that he would bring these too from maaser sheni money, it does not work. The todah and its bread he may bring from what was purchased with maaser sheni money, but he is still obligated to spend from his own pocket, from chulin money, to purchase the fine flour, the oil and the wine of the nesachim.
And why? Because, as was explained in the previous Mishnah, the scope of what maaser sheni money may be used for is limited to purchasing things needed by the person himself, that is, things that are eaten. Therefore a person cannot use maaser sheni money to pay for his lodging expenses when he goes up to Jerusalem, and likewise he cannot use it to buy nesachim - for what is done with the nesachim? The meal offering of the nesachim is burned on the altar, and the wine is poured into the hole at the top of the altar and from there into the shittin beneath the altar, and the person does not eat them. Since the nesachim are not eaten by the owner, he cannot use maaser sheni money for this purpose.
This is what the Mishnah means when it says: "Unesachim bechol makom" - in every case, whatever the wording of his obligation may have been, he will always be required to bring the nesachim "lo yavo'u ela min hachulin" - from his own private funds alone and never from maaser sheni, since maaser sheni is not used to purchase things that are not eaten.