The roles of the notary

"The more notary, the less judge"

With these words the famous jurist Carnelutti defined the essence of the notary's role (and therefore his most important activity before the law).
The meaning is that the better the notary does his job - of verifying and interpreting the wishes of parties (i.e. persons) in the drafting of a contract and the drawing up of the relevant clauses in a legal manner - the less likelihood of having recourse to the judge (and in other words the less risk of the notarial document being cause for lawsuits). This is why a notary may not receive deeds expressly forbidden by the law (article 28 of notarial law) and has an obligation to be certain of the identity of the parties (article 49 of notarial law) and to ascertain in person their wishes (article  47 of notarial law).
Such obligations are particularly strict, and their non-observance entails, over and above civil responsibility, the professional responsibility of the notary (who may be suspended or in the worst case removed form practice) and may also entail criminal liability (for the offence of falsification of a public deed). A notary is a public official authorized to draw up deeds both between living persons (i.e. sales, exchanges, divisions of property, loans etc)  and last will and testaments, witness them publicly, keep and issue copies, certificates (i.e. summaries) and extracts (i.e. partial copies) (article 1 of the  notarial law).
A deed drawn up by a notary is a public document, because the notary is authorized to bear witness to it (hence he is a public official)  As such it carries particular legal force: statements made in a notarial deed (e.g. that the document has been read to the parties, or that a person has made or signed a declaration in his presence) provides full evidence (in other words must be considered as true, even by a judge), unless falsification has been proved.
The law calls for notarial deeds for those events and contracts for which it is necessary to guarantee the maximum degree of legality in terms of identity of the parties and conformity to their wishes, because such acts are considered significant: for their social and economic content or complexity (e.g. sales, divisions of property, loans and other real-estate contracts, deeds of constitution of commercial companies and modifications to social status, constitution of associations for the purpose of becoming juridical entities, etc); for the effects they may have upon the civil status of a person (e.g. recognition of a natural child); and for the public interest in the expression of a person's will and its accurate rendering in legal language (e.g. wills, donations).