The korban Pesah is unique among the sacrifices in a number of ways, some of which are discussed on our daf. For example, our Gemara discusses the case of a korban Pesah that was not sacrificed at the appropriate time – the afternoon of the 14th of Nisan – but rather on some other day during the year. In any other situation, the sacrifice would simply be invalid. There is, however, a special rule with regard to the korban Pesah: it can be changed from a korban Pesah and sacrificed as a Shelamim. There are a series of discussions in the Gemara that revolve around the question of how the Pesah can be changed to a Shelamim – if the very fact that the Pesah is not being carried out properly switches it to a Shelamim, of if it is necessary to consciously substitute one intention for the other.
The possibility of changing the korban to a Shelamim may be connected with the fact that, unlike most other sacrifices, the Shelamim is almost never brought because one is commanded to do so; rather it is a korban that is given freely as a toda – thanksgiving offering – or a nedava – a voluntary offering (see 7:11-12, 16).
There is a difference of opinion among the rishonim regarding the meaning of the name shelamim. Rashi (Vayikra 3:1) cites two opinions:
a. that this korban spreads peace in the world;
b. that they bring peace to the altar, to the priests, and to the owners (i.e. that all three parties to the sacrifice benefit from the eating of the sacrifice).
Another rule unique to the korban Pesah is the need to participate in it as a formal member of a group; one must “sign up” before the holiday in order to join (see Shmot 12:4). When the korban itself is eaten – that is to say, during the Pesah as it was practiced during Temple times – a person was not allowed to leave his or her group and join another, unless he/she joined another group before the sacrifice was slaughtered.