(a) The Avoda of Korban Pesah as described in the Mishna has one Kohen doing the Kabala, the Holacha being done by a chain of Kohanim, and at the end - another Kohen doing the Zerika.
Ordinarily we could understand Mehashvin me'Avoda le'Avoda to mean that if one Kohen has a improper thought at the Kabala it may invalidate an Avoda
that he does later. However, when we say Mehashvin me'Avoda le'Avoda this works out - in the Korban Pesah - that one person's thought determines the validity of a second persons act, even though the second person not only acted properly but also did NOT do anything to invalidate his activity!
If Kohen 1 thought that Kohen 2 should do something wrong - why does that thought apply AT ALL??
(b) The same question could be asked:
How does the wrong thought of the owner apply to the Avoda of the
Kohanim - but the owner clearly has more powers with the Korban
than a Kohen whose involvement is only that of a Shaliah.
Therefore we should have two sources: a source for the owner (that his thoughts invalidate the Avoda of the Kohanim) and then for the Kohen (to invalidate the Avoda of another Kohen).
We could say: if we assume that the improper thought of the owner is valid - since he is the owner(?), and the Kohanim are Shelihim - if we say that the rule Shaliah Oseh Shaliah applies here, and the second Kohen is only the Shaliah of the first - we could also understand the invalidation-at-a-distance! But I feel this is a bit far-fetched.
So I remain with my query:
Wherefrom do we derive the empowerment of the improper action-at-a-distance from one person to another?
Yeshayahu HaKohen Hollander
(a) The Gemara means that the Kohen who slaughtered the animal thought, "I hereby am slaughtering this Korban with intention that its blood be Nizrak, either by me or by someone else, with a Machshavah of Pigul."
Even though the Kohanim stand in rows performing the Avodah, it is possible that this Kohen intended to leave his row and to do the Zerikah himself. Even though he did not, in the end, leave his row, the Korban is already Pasul because of his Machshavah.
Even if he thought that someone else would do the Zerikah, Hagaon Rav Moshe Sternbuch told me that it will still be Pasul, because it does not matter that the other Kohen did not have any Machshavah. It was the Machshavah of the Shochet that invalidated the Korban, and not that of the Zorek. A Machshavah during Shechitah concerning the Zerikah invalidates the Korban because of the principle "Mechshavin me'Avodah le'Avodah."
(Perhaps your question depends on whether the Machshavah of slaughtering the animal with intention to do the Zerikah at an improper time is a Pesul in the Shechitah or in the Zerikah. We mentioned this point in Insights to 61:2).
(b) Regarding whether the Machshavah of the Ba'alim is able to be Machshir or Posel the Korban and to override, as it were, the Machshavah of the Kohen, this is a Machlokes Tana'im in Zevachim (47a).
Be well, Mordecai