Shekalim, Chapter 4, Mishnah 9. The Mishnah opens: "Achas lishloshim yom mesha'arin es halishkah" - once every thirty days they set the rates for the chamber, that is, the room in which the shekels were kept. The intent is not to appraise the chamber itself, since it contains nothing but coins, but rather to appraise what is going to be purchased with the money in it: they fix a set price for the wine, the oils and the fine flour that are going to be used, whose purchase is funded from the chamber.
The purpose of this is to establish a binding price: this is the price that will be paid to the suppliers for the items the Temple treasury needs. However, if the price drops, the treasury always benefits and receives the lower price, as will be explained shortly.
"Kol hamekabel alav lesapek selasos":
The Mishnah continues: "Kol hamekabel alav lesapek selasos" - anyone who undertakes the responsibility of supplying fine flours, that is, the high quality flours, to the Temple. Here two situations are distinguished:
"Me'arba ve'amdu mishalosh - yesapek me'arba": he agreed to supply four measures (se'ah) per sela, and afterwards the market price rose, so that a sela buys only three. Even so, the supplier must supply at the rate of four, since the calculation was made for thirty days and one must hold to it.
"Mishalosh ve'amdu me'arba - yesapek me'arba": he agreed to supply three se'ah per sela, and afterwards the price dropped, so that a sela buys four measures - we follow the cheaper price.
And the reason for this, in the words of the Mishnah: "Mipnei sheyad hekdesh al ha'elyonah" - the hand of the Temple treasury is always the upper hand.
Understanding "yad hekdesh al ha'elyonah":
Hekdesh is unique in the laws of acquisition. An ordinary person does not acquire and does not gain ownership of an object through money alone; regarding hekdesh, however, it says "venasan es hakesef vekam lo" - that its acquisition is effected through the transfer of money. Therefore, since the treasury paid the sum in advance for the coming month, it is already the owner of the merchandise at the price that was fixed, and it is not required to add anything when the price rises.
On the other hand, it would not be fitting for the power of hekdesh to be weaker than that of an ordinary person, whose acquisition is effected by pulling the item. The treasury has not yet pulled or actually taken possession of the entire month's supply, and an ordinary person who is not yet the owner would receive the cheaper price if the market price fell. For that reason we do not place hekdesh in a worse position than a private individual; and on the other side its advantage is preserved, that if the price rose it adds nothing, since it already acquired through the acquisition of money. This is "yad hekdesh al ha'elyonah."
The supplier's responsibility for spoiled merchandise:
The Mishnah continues: "Hisliya solet - hisliya lo, hechmitz yayin - hechmitz lo" - if the fine flour became wormy, the loss is the supplier's; if the wine soured and turned to vinegar, that too is his responsibility. Although the treasury acquired to a certain extent, it acquired only partially - only as to the advantage, but as to the liability it did not acquire.
And the Mishnah concludes: "Ve'eino mekabel es me'osav ad sheyehei mizbe'ach meratzeh" - the supplier does not receive his money, meaning he has no certainty that the money is fully his, until there is appeasement (atonement) on the altar, that is, until the offering is actually brought. Only at that moment can the supplier be assured that a valid sale took place here.
In summary: In this Mishnah we learned that once every thirty days they set the rates for the chamber and fix a set price for fine flour, wine and oils. A supplier who undertook to supply at a certain rate - if the price rose, he supplies according to the original rate, and if the price dropped, he supplies according to the cheaper rate, because the hand of hekdesh is the upper hand: the acquisition of hekdesh is effected with money ("venasan es hakesef vekam lo"), and we do not place it in a worse position than a private individual who acquires by pulling. Nevertheless, spoilage of the merchandise - flour becoming wormy and wine souring - is the supplier's responsibility, and his money is not secured in his hand until there is appeasement on the altar.