If we only operate with a 27 book Bible we rob ourselves of the roots and foundations on which the gospel stands. Our gospel will be flimsy and appear 'new' when it is rooted in everything God has ever said, the God who reveals all this plans. Amos 3v7: For the Lord GOD does nothing without revealing his secret to his servants the prophets. That's spoken into a context where God's people were silencing their prophets, and so robbing themselves of the life-giving knowledge of God. We do the same to ourselves if we silence the law and the prophets by not permitting them to sing their true melody, about the Christ.
I want to thank Ed Goode for the prompt to write on this theme this week over at Digital H2O.