"For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book." (Revelation 22:18)
This very sober warning right at the end of the Bible was given by Christ Himself (note verse 20) to indicate that the written Scriptures were now complete, and it would be a serious sin for some pseudo-prophet to come along presenting some alleged new revelation from God. That this warning applies to the entire Bible, not just to the Book of Revelation, should be obvious, but is made especially clear when it is remembered that Jesus promised His chosen disciples that the Holy Spirit "shall teach you all things, and bring all things to your remembrance," and furthermore, that "he will guide you into all truth: . . . and he will shew you things to come" (John 14:26; 16:13).
This special revelation to the "apostles and prophets" of the New Testament would constitute the "foundation" of the church, and would be complete when the last of these "holy apostles and prophets" were gone (study carefully Ephesians 2:19-3:11). When John completed the Apocalypse, he was very old; all the other apostles and prophets of the New Testament had already died (all by martyrdom), so God's written Word was now complete. No new revelation would be needed before Christ returns. We shall do well if we just learn what we already have received from His holy apostles and prophets.
Note also the emphasis on "the words," not just the concepts. God was able to say what He meant and we are wise if we take His words literally. Jesus warned about "false prophets" who would come after He left (Matthew 24:24), and there have been many of these through the centuries. The Bible as we now have it is sufficient for every need. HMM