At first it almost seems as if John Piper has said something quite profound. And maybe he has if you are an English major... However if your more concerned with theology then Mr. Piper has completely missed the point.
The point is stated much better by Pope John Paul II,
“Further along, the council remarks that the catholic Church rejects nothing that is true and holy in these (other) religions. The church has a high regard for their conduct and way of life, for those precepts and doctrines which, although differing on many points from that which the church believes and propounds, often reflect a ray of that truth which enlightens all men. However, the Church proclaims, and is bound to proclaim, that Christ is “the way the truth and the life” (John 14:6), in whom God has reconciled everything to himself. The Church is guided by the faith that God the Creator wants to save all humankind in Jesus Christ, the only mediator between God and man... The holy Spirit works effectively even outside the visible structures of the Church.”
-Pope John Paul II Crossing the Threshold of hope
The popes approach seks to avoid twin dangers . On the one hand he avoids a relativistic solution. He doesn't say "Everybody's okay, it doesn't matter what you believe - just believe somthing." On the other hand, he seeks to avoid a divisive tone. This is essential because in a world torn by division and hatred, people instinctively feel that a faith that adds to the division , that fules the hatred, that erects barriers rather than bridges, is part of the problem not the solution.
The goal is not doctrine! And one of the worst things we can do as humans is think we can build a doctrinal structure that can hold the creator of the universe. Seriously do you believe we can completely understand God? And even if we could (which we can't), do you believe we could flawlessly put it on paper and teach it to others.
Now some make the argument that the bible as Gods divinely inspired word describes God. But the bible is not doctrine! The Bible is the story of God reaching out to humans... Doctrine is our attempts to reach him, our Tower of Babble .
Deadly indeed, Deadly to our institutions. But it is a breath of fresh air for the organic church.
** Please note this is not a jab at John Piper. After reading some of his other books I believe his heart is in the right place. However Like most of us sometimes he misses the point.**