Justin Taylor links to an e-mail from NT Scholar to Mark Driscoll in discussing contextualization, the missiological principle of communicating the unchanging gospel in ways understandable in a certain cultural context. I'll reproduce the quote here:
Paul refuses to circumcise Titus, even when it was demanded by many in the Jerusalem crowd, not because it didn’t matter to them, but because it mattered so much that if he acquiesced, he would have been giving the impression that faith in Jesus is not enough for salvation: one has to become a Jew first, before one can become a Christian. That would jeopardize the exclusive sufficiency of Jesus.
To create a contemporary analogy: If I’m called to preach the gospel among a lot of people who are cultural teetotallers, I’ll give up alcohol for the sake of the gospel. But if they start saying, “You cannot be a Christian and drink alcohol,” I’ll reply, “Pass the port” or “I’ll think I’ll have a glass of Beaujolais with my meal.” Paul is flexible and therefore prepared to circumcise Timothy when the exclusive sufficiency of Christ is not at stake and when a little cultural accommodation will advance the gospel; he is rigidly inflexible and therefore refuses to circumcise Titus when people are saying that Gentiles must be circumcised and become Jews to accept the Jewish Messiah.
The quote is from an upcoming book entitled The Supremacy of Christ in a Postmodern World