It refers to a superior giving orders to an inferior, it is an officer giving orders to a soldier. It is an aggressive, definitive statement of absolute authority calling for behavior that requires obedience. Secondly, it is used in legal terms. There are some ancient papyri in which parangello is used of summoning a man to court. He is thereby bound by legal injunction against him to obey and respond.
Some secular sources use the word in ethical matters.
For example, Aristotle teaching morals or ethics which become binding on the individual who has any integrity. It is also a word used to define certain techniques. For example, it is used of the rules of grammar and oratory, or the rules of literary composition. In summary, it defines precise behavior exactly how something is to be done. It is also a medical term, used of a doctor prescribing medicine for someone who is sick, and wants to be well.