John Piper is having Rick Warren speak for his fall, 2010 Desiring God conference because Piper says Warren is a solid, Biblical, evangelical. Yet, Rick Warren's website is currently promoting and recommending books by Richard Foster. One of the books is entitled, Celebration of Discipline: The Path to Spiritual Growth. This book does not promote the Biblical idea of "Scripture alone." Foster calls on Christians to be involved in mystical practices in order to connect to God and to discover new revelations. The Biblically minded Christian knows that all the Christian needs to do is study the Bible and rely on the ministry of the Holy Spirit to assist us in understanding. Foster's book among other things encourages Christians to be involved in Transcendental Meditation. Foster denies that he is promoting TM but yet admits that he is calling on Christians to "empty the mind in order to fill it." Foster also encourages Christians to enter the world of mediation through the door of imagination. The Bible has fourteen verses in the King James Version that speaks of the imagination and all of the verses speak of it in a negative manner. Foster claims that Christians, through their imagination, can actually encounter the living Christ and that he will "actually come to you." However, Foster also warns that what he is encouraging Christians to do can be dangerous. Foster says "…since to open ourselves to spiritual influence can be dangerous as well as profitable." Foster claims Christians need to be taught by "masters" who are Christians that have learned the art of mediation techniques. Foster also encourages Christians to be involved in astral projection. Foster says that is not what he is promoting but it clearly is when Foster writes, "In your imagination allow your spiritual body, shinning with light, to rise out of your physical body. Look back so that you can see yourself laying in the grass and reassure your body that you will return momentarily. Imagine your spiritual self, alive and vibrant, rising up through the clouds and into the stratosphere…Go deeper and deeper into outer space until there is nothing except the warm presence of the eternal Creator." Does John Piper agree with Richard Foster? If not then why is Piper praising Rick Warren as a Biblical pastor and having Warren speak for his conference when Warren's website is promoting Foster's books that are filled with the mysticism of pagan spirituality?