... and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book. (Revelation 22:19)
From the Mormon founder Joseph Smith, to Muhammad, to various cults, and to individual Popes and the Catholic Church, history has recorded an assortment of people and groups over time have asserted there are NEW teachings that God has supposedly given them to ADD to or make changes to (or to contradict) the Bible as it was ALREADY completed after the last apostle died. But the Bible itself - and notably the Apostle Paul - have given severe warnings about making such changes or additions. In fact, Paul declares that NO one has been given the authority or right to change what God gave us through His Son Jesus and the inspired writings of His prophets and apostles - not even Paul himself! See here for one of the Bible's most important teachings on this issue: https://www.youtube.com/shorts/q5lKkSN99CA
Galatians 2:6: As for those who were held in high esteem—whatever they were makes no difference to me; God does not show favoritism—they added nothing to my message.
Proverbs 30:5-6: Every word of God proves true; he is a shield to those who take refuge in him. 6 Do not add to his words, lest he rebuke you and you be found a liar.
Deuteronomy 4:2:You shall not add to the word that I command you, nor take from it, that you may keep the commandments of the Lord your God that I command you.
And, of course, Revelation 22:19 warns of severe consequences of adding to or taking away from what God has communicated through His Scriptures: Revelation 22:19: ... and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book.