A notary public is a public servant who must provide services to any person that makes a reasonable and lawful request. The notary public is not permitted to limit services to a particular group of people even if it is limited to just to the people who the notary public interacts with at work.
A notary public is not a licensed attorney, is not authorized to practice law, and is not allowed to give any legal advice. That is, of course, unless the notary public also happens to be an attorney. This includes advising clients of the contents of the document.
Notary publics have a long and rich history in human society. Notary publics have been around since the Roman Empire. The services have changed over the years, but the role has been needed for a long time.