While the Temple stood, a person could donate to the Temple by consecrating an animal to be sacrificed on the altar or by sanctifying an object of value that will become the property of the Temple. In the first case there is inherent sanctity (kedushat ha-guf), and the animal must be sacrificed – unless it develops a permanent mum, or blemish. In the latter case, only the value of the object is holy (kedushat damim) and the Temple treasurer can sell the object or use it in some other way that will benefit the Temple.
The Mishnah on today’s daf (=page) discusses a situation where someone sanctifies a female animal to be brought as an asham – a guilt-offering. This presents a difficulty, since guilt-offerings can only be brought from male animals. The Mishnah rules that we wait until the animal develops a permanent blemish, and at that time it can be sold and a replacement asham must be purchased with the proceeds.
The Gemara questions the logic of requiring that we wait to sell the animal until it develops a mum. Surely the fact that its physical make-up prevents it from being brought as an asham should be viewed as a permanent blemish, which would allow it to be sold immediately!? Rav Yehudah quotes Rav as explaining that in a case like this one, the kedushat damimon the animal gives it a level of kedushat ha-guf, so that it cannot be sold unless it has a true blemish.
This explanation leads Rava to conclude that if an animal that is fit for sacrifice is consecrated for its value (kedushat damim) it automatically receives inherent consecration (kedushat ha-guf) and will have to be sacrificed, rather than sold.
This rule applies not only when the person specifies that the value of an animal is meant to purchase a sacrifice, and the requirement is to bring that animal rather than selling it and purchasing another, but even in a case where someone consecrates all of his possessions to the Temple, all animals that are fit for sacrifice should be brought as korbanot.