Menachos 9 - 15
When Flesh and Fat Combine
When the blood of an animal sacrifice is applied to the altar it serves as a catalyst for the fatty parts of the sacrifice (cheilev) to be burned on the altar and for the flesh of the sacrifice to be eaten.
What if both the fatty parts and the flesh disappeared before the blood was applied to the altar?
The rule stated by Rabbi Yehoshua is that at least a kezayis (olive-size) of either flesh or cheilev must remain intact in order for the blood application to take place. Otherwise it serves no significant purpose and cannot be performed.
Even if there is half a kezayis of flesh and half a kezayis of cheilev the blood is not applied to the altar for we cannot combine the altar's consumption with human consumption. But if the sacrifice in question is an olah which is completely consumed upon the altar the blood will be applied even if only half a kezayis of flesh and half a kezayis of cheilev remain. The reason is that in the case of the olah, flesh and cheilev are both consumed upon the altar and are therefore considered one entity.
- Menachos 9a
A Sacred Shortcut
In the sanctuary service of offering a mincha (a meal offering) a kometz (a palm-full of meal) is taken from the mincha and brought to the altar to be burned. Then the frankincense on the mincha is gathered and also burned on the altar while the remaining meal is consumed by the kohanim.
What if a non-kohen gathered this frankincense and handed it to a kohen to burn on the altar?
Rabbi Yannai ruled that this would be invalid since performed by a non-kohen.
The question arises, however, as to why such a seemingly inconsequential action as gathering the frankincense should be valid only if a kohen performs it.
Rabbi Yirmiyahu points out that both in regard to animal sacrifices and mincha offerings the relaying of something to the altar is considered an essential part of the service which only a kohen can perform. In the case of the animal it is relaying the blood to be applied to the altar; in the case of the mincha the relaying of the kometz of meal or the frankincense to be burned on the altar. Although the non-kohen fails to take a single step his gathering of the frankincense and handing it to the kohen reduces the distance which the kohen would have been compelled to walk in order to perform the service of relaying this frankincense to the altar and it is therefore considered an integral part of the service which is invalid when performed by a non-kohen.
- Menachos 13b