The first reason why I think we love him is because he knows how to tell people about Jesus. Seems pretty simple but it ain't as simple as we'd like to think, that's why we like him.
The scientists tell me that climate change is real and it's happening, in the Christian world, climate change happened a while ago. Hauerwas reckon that change occurred on a Sunday night in 1963 when a local picture theatre dared to open on a Sunday night. Whether it was then or sometime about then, Christianity was getting voted off the island.

Until then, Christianity had lived the good life for many years. Almost everyone was a Christian of some sort or other. Clergy were respected the church was a powerful social force in society. Being a Christian meant that your opinion mattered, rather than being automatically irrelevant. All of this was changing. It was the beginning of the end of Christendom. Christianity had lost its pride place at the table of Western culture.
'The world can no longer be divided into “Christian” and “non-Christian” territories separated by oceans.' (Bosch, Transforming Missions, 3)
Like a frog in slowly boiling water, Christians were slow (and some still haven't) to realise the danger.
Keller is a guy who seems to have got it. He's a guy who seems to have seen the shift and has worked out how to do church in a post-Christian world. Keller knows how to tell post-Christian and post-Modern people about Jesus. And that is one reason why we like him.
You can hear it in his preaching. You can see it in his church planting. He seems to be on to something, and we all (for very good reason) want a piece of the action.
Why do we love Keller? He knows how to tell people about Jesus.
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Picture from Fox Theatre St Louis.