By the phrase 'the end of apologetics', Penner means that the main approach to apologetics that is advertised, marketed, and conducted through debates and in books is misguided. To quote:
So it is that many attempts to articulate the reasonableness of Christian faith in our context paradoxically end up doing something different than defending genuine Christianity.
I agree. I did not find them helpful when I was in college and undergoing a change in my thinking. In my twenties I read Francis Schaeffer and heard Josh McDowell but did not find in them what I'd hoped. C. S. Lewis' Mere Christianity was the best thing but it was not enough to satisfy my struggles.
Penner goes back to the mid-19th century Christian writer, Soren Kierkegaard, for guidance and builds upon his insights. Kierkegaard diagnosed some of the same problems even in his day and time. An aside here, it is my impression that K is written off by many conservative/evangelical Christians because he is identified as an existentialist and is hence basically wrong. I was briefly introduced to K in the spring of 1971 when I took a Philosophy of Religion course at Harding University. We discussed him and I remember the teacher saying that reading him was a boring and good for putting one to sleep. That colored my thinking about K till the last decade. I still haven't tackled his writings but his name and influence keep coming up in meaningful and insightful things I'm reading. I keep coming across pithy quotes that capture and convey wonderful insights. And then he provides inspiration for wonderful books such as this one.
I'll close this post with another quote from the introduction.
I begin by noting that the goal of traditional apologetics is to justify the objective truth of the propositions of Christian doctrine. Christianity, the "essentially Christian," is therefore assumed, implicitly or explicitly, to be captured in these propositions. The Christian truths defended by such modern apologetics are taken to be ahistorical, unsituated, abstract, and universal. I then use Kierkegaard's concept of truth as subjectivity to launch a critique on apologetic propositionalism and to provide an alternative way to think about Christian truth.