Shevi'is Chapter 10, Mishnah 3. In the previous mishnah we examined the concept of one who hands over his notes of debt to beis din: a person who gives his promissory notes into the hands of beis din is not subject to the laws of the cancellation of debts, and he may collect his loans even after the shemittah year has ended. This mechanism is the foundation upon which the innovation presented in our mishnah is built - the prozbul.
The words of the Mishnah:
"Prozbul eino meshamet" - loans for which a prozbul was written are not subject to the law of the cancellation of debts, and the lender may collect them after shemittah.
The enactment of Hillel the Elder:
The Mishnah adds that this is one of the things that Hillel the Elder enacted, when he saw "shenimne'u ha'am mil'halvos zeh la'zeh" - that people were refraining from lending money to one another, and by doing so they were transgressing what is written in the Torah in the book of Devarim: "Hishamer lecha pen yihyeh davar im levavcha beliya'al". The Torah warns that a person should not allow a negative thought to arise in his heart, as the verse continues: "karvah shenas hasheva" - that is, out of concern that shemittah is approaching and the loan will be cancelled, a person refrains from lending. The Torah warns that refraining from lending for this reason is a transgression, and nevertheless people were violating it.
The basis of the enactment:
What did Hillel do? He enacted the prozbul. The basis of the prozbul lies in the concept of handing over one's notes to beis din mentioned above: the law of the cancellation of debts was stated regarding "re'echa" (your fellow), and it does not apply to beis din. Therefore, when beis din is responsible for the loan, the cancellation of debts does not apply to it. The prozbul, then, is the formula through which a person hands over his notes of debt into the hands of beis din.
The meaning of the word 'prozbul':
The word itself is made up of two parts:
'proz' - an enactment, a way of remedying a situation.
'bul' - a term whose meaning is wealthy people.
In other words, an enactment for the wealthy, so that they will not transgress the Torah's prohibition of being unwilling to lend money. The enactment remedies their situation and enables them to continue lending, without losing their money.
In summary: In this mishnah we learned that a prozbul is not cancelled, and that this enactment is one of the enactments of Hillel the Elder, which came to prevent the transgression of the Torah's warning "Hishamer lecha pen yihyeh davar im levavcha beliya'al". Its basis is the handing over of the notes of debt to beis din, since the cancellation of debts was stated regarding "re'echa" and not regarding beis din, and even its name teaches us its essence: an enactment for the wealthy, enabling them to continue lending.