This past week I came across a series of video conversations between Carson, Piper and Keller on the Gospel Coalition website (I'm not sure when they originally were posted). There are ten "chapters" in all:
Of these ten, I found chapters 1, 5, 7, and 9 to be most helpful. But if you can only watch one, I would recommend chapter 9, where Piper and Keller interact on how "God-centered" and "gospel-centered" connect. In the course of this interaction, Piper admits that his language of being "God-centered" at times has not been "Christ-centered" enough. But Keller also admits that in his emphasis on being "gospel-centered" that his language could be misunderstood to be strictly cognitive rather than penetrating to the affections. To whet your appetite, here is a snippet of Piper that captures it well:
"The apex of the glory of God is seen in Christ, and the apex of His glory is seen in the cross, and therefore to be God-centered leads to Christ-centered leads to cross-centered."