In these verses we see a) that the Gospels of the Bible are revelations by Jesus Himself and b) that God warns us about a different gospel message from an angel from heaven.
There are no verses anywhere in the Bible that state there will be additional written revelations after the book of Revelation. Since Revelation deals with events clear up to the very last days, no additional revelations are needed. On the flip side, as we saw above, there are explicit warnings not to add or subtract anything to the last book of the Bible, Revelation. Additionally, several old and new testament books in the Bible do predict additional false revelations from Satan, demons and human false prophets including in the last days.
The purpose of these additional extra-Biblical revelations are to mislead people away from the central truths of the Bible's Gospel message of salvation by faith in Jesus Christ (as the Bible defines it). In addition to the Galatians verse above, these other Bible verses are examples of warnings about false doctrines that originate from extra-Biblical revelations and false prophets:
Now the Spirit speaketh expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils; 1 Timothy 4:1
And many false prophets shall rise, and shall deceive many. Matthew 24:11
For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if [it were] possible, they shall deceive the very elect. Matthew 24:24
For such [are] false apostles, deceitful workers, transforming themselves into the apostles of Christ. And no marvel; for Satan himself is transformed into an angel of light. 2 Corinthians 11:13-14
But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction. 2Peter 2:1
This is an important point because books like Urantia and the Book of Mormon claim to be additional revelations. They also claim to have originated from spirits claiming to be from Heaven. In stark contrast, not one book of the Bible was authored by an angel or from a human that was being inspired to write what he did by an angel. God Himself (the Holy Spirit) directly inspired all of the human authors of the Bible or they got the information first-hand from Jesus Himself.
Proof that the Human authors of the Bible were inspired by God
And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. All scripture [is] given by inspiration of God, and [is] profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, throughly furnished unto all good works. 2 Timothy 3:15
It is interesting that one of the most common reasons for trying to deny the authority of the Bible is actually one of the strongest reasons for proving it’s divine inspiration and authenticity. How many times have you heard that the Bible can’t be trusted because it was written by mere men? It’s a common straw man argument that many atheists, agnostics and cults use to try to deny it’s authority and accuracy. But when considering the following facts, it's God-inspired human authorship is actually a strength, not a weakness:
Collectively it was written over about a 1,500 year period. It had about 40 different authors. Yet in spite of that, the old testament books are in complete harmony with the new testament books. This is quite remarkable when you consider how difficult it would have been for 40+ men to have perpetrated a hoax as complex and wide-spread as the Bible over a 1,500 year period, and the fact that many of the Bible's authors died a martyr's death because of their absolute belief in it's authenticity.
Numerous scientific facts that modern science didn’t discover until many centuries later appear in the Bible. Given the fact that jets, submarines and other modern technology were in rather short supply during Biblical times, how were mere human authors able to know these things with virtual 100% accuracy? For some examples of this scientific foreknowledge, see:
http://Creationists.org/foreknowledge.htmlThe Old Testament contains about 300 prophecies about the Messiah, Jesus. Just eight of these prophecies were examined in the book Messages from Heaven (See pages 58-61 of the book). The entire book can be read on-line at:
http://www.harpazo.net/EternalProductions/ApparitionsofMary/MFH.pdfThey calculated the statistical odds that just these eight prophecies would come true and it turned out to be one in 10,000,000,000,000,000,000,000,000,000. That staggering number is even more amazing when you consider that there were about 290 more prophecies that also came true that they didn’t factor into the equation! It simply would have been impossible for mere men to have prophesied these things or even conspired with others many centuries after they had died to somehow "make" these things happen the way they did. The authors who wrote these prophecies were clearly inspired by God to write what they did. We can be certain that demons did not feed them this information because one test of whether prophecies are from God or from demons is the 100% accuracy test (Deuteronomy 18:22). Satan can get it right sometimes, but not always. The Bible authors had a perfect record.
There are many prophecies about the last days. It certainly appears that a good number of them are coming true in this generation. The prophecies about Israel are especially stunning. For more information about these prophecies, see the video Countdown to Eternity at this link:
http://creationists.org/countdown_to_eternity/english.html