Some Emerging Church Christians believe there are radically diverse perspectives within Christianity that are valuable for humanity to progress toward truth and a better resulting relationship with God, and that these different perspectives deserve Christian charity rather than condemnation. Reformed and evangelical opponents, like John MacArthur, do not believe that such generosity is appropriate, citing the movement's shift away from traditional evangelical beliefs such as eternal punishment and penal substitution towards a reintroduction of, for example, elements of ancient mysticism. Movement leaders such as Rob Bell appropriate set theory as a means of understanding a basic change in the way the Christian church thinks about itself as a group. "Set theory" is a concept in mathematics that allows an understanding of what numbers belong to a group, or set. A bounded set would describe a group with clear "in" and "out" definitions of membership. The Christian church has largely organized itself as a bounded set, those who share the same beliefs and values are in the set and those who disagree are outside. The centered set does not limit membership to pre-conceived boundaries. Instead a centered set is conditioned on a centered point. Membership is contingent on those who are moving toward that point. Elements moving toward a particular point are part of the set, but elements moving away from that point are not. As a centered-set Christian membership would be dependent on moving toward the central point of Jesus. Christians are then defined by their focus and movement toward Christ rather than a limited set of shared beliefs and values. John Wimber utilized the centered set understanding of membership in his Vineyard Churches. The centered set theory of Christian Churches came largely from missional anthropologist Paul Hiebert. The centered set understanding of membership allows for a clear vision of the focal point, the ability to move toward that point without being tied down to smaller diversions, a sense of total egalitarianism with respect for differing opinions, and an authority moved from individual members to the existing center. The movement favors the sharing of experiences via testimonies, prayer, group recitation, sharing meals and other communal practices, which they believe are more personal and sincere than propositional presentations of the Gospel. Teachers in the emerging church tend to view the Bible and its stories through a lens which they believe finds significance and meaning for their community's social and personal stories rather than for the purpose of finding cross-cultural, propositional absolutes regarding salvation and conduct. The emerging church claims they are creating a safe environment for those with opinions ordinarily rejected within modern conservative evangelicalism and fundamentalism. Non-critical, interfaith dialog is preferred over dogmatically-driven evangelism in the movement.