Menachos Chapter 13, Mishnah 3. From the menachos we move on to other types of voluntary offerings. The Mishnah opens with a person who says "Harei alai eitzim" - "I take upon myself to bring wood" - he obligates himself to bring wood to the Beis HaMikdash. The word "eitzim" can mean either trees or pieces of wood, and in our context it refers to pieces of wood. Since he used the plural, we cannot interpret his words as referring to a single piece, and therefore "lo yifchos mishnei gezirin" - he must bring at least two logs.
What are the 'gezirin':
'Gezirin' are the type of logs that were used as fuel for the arrangement of wood on the outer Altar. The Gemara describes them as a sort of disc cut from a tree trunk, an amah by an amah in length and width, and as thick as the stick used to level off a heap of grain (the exact measure of this thickness is not precisely known to us), and this is also the ruling of the Rambam. So we are speaking of two wooden discs measuring an amah by an amah.
What is the nature of the wood offering:
The Gemara wonders about the essential nature of this offering, and the Tannaim disagree about it: is this wood meant to fuel the fire, or is it wood that goes up on the fire like any other offering?
The view of Rebbi (Rabbi Yehudah HaNasi): This wood is an offering that goes up on the fire, exactly like all other offerings brought up on the Altar. According to this view, one must produce a kometz of sawdust from the wood and bring it up on the Altar as part of the offering, and even salt it as is done with a regular offering.
The view of the Chachamim: There is no new, separate offering here called a 'wood offering'; this is simply wood for the fire. Within this view there are two approaches:
Some understand that the one who obligates himself creates only kedushas damim - he is donating to pay for the wood of the arrangement, and therefore the wood can be redeemed, its value transferred to something else, and that item brought up on the fire.
Others understand, as Rabbeinu Yerucham holds, that this is an obligation to actually bring the wood for the arrangement. The 'gezirin' are the logs used for the arrangement, and therefore he brings at least two logs, which go up on the arrangement to fuel the burning fire.
"Harei alai levonah":
One who says "Harei alai levonah" - "I take upon myself frankincense" - obligates himself to bring frankincense. Here too, as with the wood, this is an offering that stands on its own - frankincense by itself, and not as an accompaniment to a particular minchah - and this possibility is derived from a verse. And how much must he bring? "Lo yifchos mikometz" - not less than a kometz. Since he did not specify a particular quantity, he must bring at least one kometz - a handful, three fingers' worth - which is the measure used for other offerings, and we follow that standard.
There are five kematzim:
The Mishnah adds an incidental note here: within the conceptual world of halachah there are five kematzim that carry halachic significance. They are:
One who says "Harei alai levonah": One who obligates himself to bring an offering of frankincense brings one kometz, and may not bring less than that. This is the ruling of our Mishnah.
A voluntary minchah: One who obligates himself to bring an ordinary minchah brings a kometz of frankincense along with it. The obligation of a minchah includes not only the fine flour, but its other components as well: the oil and the frankincense placed on top of it. Therefore, even if he spoke or thought only about the flour portion, the frankincense is an inseparable part of the minchah, and the kometz of frankincense comes with it.
One who offers up the kometz outside: We have already dealt with the prohibition of bamos, that one may not offer sacrifices outside the Azarah. One who offers up a minchah outside the Azarah - even though he offered it to Hashem, only that he did so in a place that is not fit for it - if the amount he offered was a kometz, he is liable to kareis.
The two bowls of frankincense: The two bowls placed upon the lechem hapanim, each of which contains a kometz of frankincense - these are the fourth and fifth kematzim.
Two questions arise here:
The first: at first glance it is puzzling that we count the frankincense on the lechem hapanim as two of the five - but in truth there are two separate kematzim there, and so we count them.
The second, and the main one: where is the most basic law of kemitzah, the one everyone knows - that a person who brings a minchah takes a kometz from the fine flour and places the kometz on the altar? That is where the kometz finds its primary expression, so why is it not counted in our Mishnah?
The Bartenura answers that this law is in fact included in our Mishnah by implication, and it is the third case: from the fact that one who offers up a kometz outside the Azarah is liable, we learn that the standard measure that is taken and brought inside the Azarah is the familiar kometz. And indeed, the two kematzim placed on the table with the lechem hapanim are two of the five.