Shekalim, Chapter 1, Mishnah 3. The Mishnah continues to deal with the timing of the events that took place during the month of Adar, and from here it returns to the central topic - the shekalim themselves.
When the tables were set up:
"B'chamishah asar bo shulchanos hayoshvin bamedinah" - on the fifteenth of Adar they would set up the tables of the money changers, men whose job was to receive the shekalim and give change to anyone who brought a sela. According to Rashi this refers to Jerusalem; the Rambam disagrees and explains that "bamedinah" means in all the cities of Eretz Yisrael, outside of Jerusalem.
"B'esrim vachamishah yashvu bamikdash" - on the twenty fifth of Adar the tables were moved to the Beis HaMikdash, according to Rashi. The Rambam, however, who explained that "bamedinah" means outside of Jerusalem, interprets "mikdash" as referring to Jerusalem.
"Hischilu l'mashken":
From the twenty fifth of Adar they began to take collateral from anyone who had not yet given his half shekel, taking from his possessions until he was ready to pay cash, since the responsibility to participate rests upon him.
"Es mi memashkenin?" - from whom did they take collateral? The Mishnah defines and limits:
"Levi'im v'Yisre'elim, gerim va'avadim meshuchrarim" - from a Levi, from a Yisrael, from someone who converted, and from slaves who were freed.
"Aval lo nashim va'avadim uketanim" - these three categories are not obligated in the first place, and therefore no collateral is taken from them at all.
And here is the reason for the exemption in each case:
Women: they are not obligated to give the half shekel, as the verse says "V'nasnu ish kofer nafsho" - a man, and not a woman.
Slaves: meaning slaves who have not been freed, who are obligated only in the mitzvos in which a woman is obligated; and since a woman is exempt, they too are exempt.
Minors: here the intention is not someone who has not reached the age of thirteen, but rather someone who has not reached the age of twenty, who is not obligated.
From here there is a discussion among the poskim as to whether someone who has not reached the age of twenty needs to daven Mussaf, since the Mussaf prayer comes in place of the communal offering that was brought from communal funds, and he did not necessarily have a direct share in them. In practice we instruct him to daven Mussaf, and it also appears that the matter covers him as well, as we will see later in our study.
Nevertheless, the Mishnah continues: "V'chol katan shehis'chil aviv lishkol al yado, shuv eino posek" - anyone who has not reached the age of twenty and whose father began to give the half shekel on his behalf, the father now has an obligation to continue doing so. Since he started, he must continue even for someone who is not obligated by law.
The Kohanim - "mipnei darchei shalom":
There is one group that, although it is obligated to give, no collateral is taken from it: "V'ein memashkenin es haKohanim mipnei darchei shalom". The meaning of "darchei shalom" here is a matter of honor: since the Kohanim themselves are the ones who actually offer the sacrifices for which the shekalim are designated, they are treated with extra respect and are not approached with the same directness, for they participate in another way.
Even so, the responsibility rests upon them as well, as we will see in the next Mishnah. And even if in the end they did not give, beis din would make a stipulation that they would automatically have a share in the offerings, so that they would not be left out. So we find: no collateral is taken from them, but they are supposed to give; and if they did not give, they still have a share in the communal offerings that were brought.
In summary: in this Mishnah we learned when the money changers' tables were set up - on the fifteenth of Adar "bamedinah" and on the twenty fifth "bamikdash" - and the dispute between Rashi and the Rambam in defining those places; the beginning of taking collateral and the list of those obligated and those exempt - women, slaves and minors under the age of twenty; the obligation of a father who began giving on behalf of his son to continue doing so; and the law of the Kohanim, from whom collateral is not taken out of respect, and who nonetheless are obligated to give and do have a share in the communal offerings.