Positive Mitzvah 145
Objects Vowed to be set aside for the Priests and the Sanctuary - "Cherem"
Leviticus 27:28 "Notwithstanding, a Cherem that a man shall vow to set aside for the L-rd..."
This Positive Mitzvah tells us that if a person declares an object or animal as Cherem, this means that he is vowing to set this object or animal aside for holy use.
That object must then be presented to the priest.
If the person says, "This object is Cherem to G-d" then the object must be given for use in the Beit HaMikdash.
Negative Mitzvah 110
We are forbidden to sell any objects or property which are designated as "Cherem"
Leviticus 27:28 "No taboo thing...shall be sold"
Any possession that a person declares to be "Cherem," is "taboo" and cannot be used by him anymore.
The objects or possessions considered "Cherem" are given to the priests and become theirs to use as they see fit (see Positive Mitzvah 145).
Once a person has declared his land or belongings as "Cherem," they fall into a special category.
This Negative Mitzvah forbids that person from selling them, even if he wishes to sell it to the treasury of the Beit HaMikdash.