21 You may say to yourselves, “How can we know when a message has not been spoken by the LORD?” 22 If what a prophet proclaims in the name of the LORD does not take place or come true, that is a message the LORD has not spoken. That prophet has spoken presumptuously, so do not be alarmed.
Deuteronomy 18:21-22 NIV 2011
I do not agree in full to what I am about to quote below (from the Roman Catholic Church) but I would like to point out that many people such as Derek Prince (who is not Roman Catholic and does not give the same details in his belief as I quote below in the same way at least) and others (who are not Roman Catholic and do not give the same details in his belief as I quote below in the same way at least)) believe that people still receive private revelation today but they do not add books of the Bible for everyone throughout the whole world to use as part of the public revelation I might not be explaining their stance fully correctly. Many people for instance have avoided death, bankruptcy, etc. in specific instances where they thought God warned them in a dream, or voice or thought/inner voice, where God directed them to do something and they obeyed, but this does not mean it should be added to the collection of public revelation for instance do not go down to such and such a place at such and such a location and time does no good after that time is elapsed. For instance one person told me they once withdrew money from a bank immediately before the bank failed saving them months of time in which they would not have had access to the money due to government take-overs, if I remember right they did this because they felt God might want them to do that but they did not go and put it in a book and say this is for the moral guidance of most of the public and should make up an additional book of the Bible.
http://www.vatican.va/archive/ENG0015/__PH.HTM said:
There will be no further Revelation
Christian faith cannot accept "revelations" that claim to surpass or correct the Revelation of which Christ is the fulfilment, as is the case in certain nonChristian religions and also in certain recent sects which base themselves on such "revelations".
http://www.vatican.va/archive/ENG0015/__PH.HTM
I believe Deuteronomy 18:21-22 is meant to be a test for those who claim to be prophets of public revelation. If someone does not go down a dark alley on a hunch and does not say, "God declared...." but keeps it to themselves in word but not in action they are not setting themselves up for death penalty on the Deuteronomy 18:21-22 basis.
Many Muslims have supposedly had dreams in which they think they saw Jesus, that might be an example of a private revelation, they are not adding a book to the public set of scripture but God might be communicating something important to them privately, I said the word "might" so I am not violating Deuteronomy 18 by mentioning this.