Humans are always changing, but God does not. ( Malachi 3:6)   Jesus said, "Heaven and earth will pass away, but my words will never pass away."  His words are recorded in the old as well as the new testament as He is the same  Lord in both. There have been some  serious attempts throughout history to get rid of the Bible or change it. None have ever  worked and they never will. That in itself is miraculous.