This post is by RJS – looking at Keller’s book, not as a pastor, an evangelist, or a theologian, but as a lay Christian who has been immersed in secular academia for 27 years as graduate student, postdoctoral scholar, and professor.
Christianity is a Straightjacket — belief in absolute truth is an enemy of freedom—it endangers our civic freedom because it divides rather than unites—it stifles creativity and growth— “Christianity looks like an enemy of social cohesion, cultural adaptability, and even authentic personhood.”(p. 37) So run the complaints of many in our educated skeptical age. Tim Keller, in Ch. 3 of The Reason for Godsuggests that “this objection is based on mistakes about the nature of truth, community, Christianity, and of liberty itself.”

Keller makes several good points in this chapter ? truth (some idea of truth) is unavoidable; community cannot be completely inclusive —and no community is; Christianity is not culturally rigid—already most Christians live in Asia, Africa, or Latin America; and freedom isn’t simple.
Let’s consider but two of these ? and related ones at that.
Every community holds its members to standards of belief and behavior —our freedom, our liberal democracy, depends on a shared and required set of beliefs and practices: most importantly the sanctity of personal choice and autonomy, a belief not shared in much of the world. A community should not be judged because it has standards for its members, rather a community should be judged on tests such as:

Which community has beliefs that lead its members to treat persons in other communities with love and respect ? to serve them and meet their needs? Which community’s beliefs lead it to demonize and attack those who violate their boundaries rather than treating them with kindness, humility, and winsomeness? We should criticize Christians when they are condemning and ungracious to unbelievers. But we should not criticize churches when they maintain standards for membership in accord with their beliefs. Every community must do the same. (p. 40)

Wow — this is a telling indictment of much of our church isn’t it?
Christianity is not a cultural straightjacket ? rather, founded on a set of core beliefs, Christianity is and always has been adaptive of diverse cultures. Cultural diversity is built into the Christian faith from the Acts of the Apostles, the epistles of Paul and on to today. We worship one God, one risen Lord, but retain our cultural differences ? every tongue, tribe, people, and nation. Greeks need not become Jews, Africans need not become Americans, Republicans need not become Democrats.
So… This leads me to ponder:
What are the key beliefs and practices ? the foundation required for membership in the community?
And
Should a Christian community maintain standards on nonessentials? If so – how?
This last is a tough one – as I am convinced that our stance on nonessentials hurts the church and hurts our witness to the unchurched. It is hard to be an effective light to the world when the light observed from the outside is the glow of a fire that burns individuals within the church.