Perhaps unsurprisingly, there's a paradox here! Kierkegaard's own indirect communication proposes that we start with the experience of those who don't believe and meet them on their own ground. His success in doing this is evidenced by the fact that, at least for some periods of the 20th century, aspects of his work became a major focus for radical thinkers of various kinds, including the non-religious and, interestingly, a significant number of Jewish thinkers (Buber, Rosenzweig, Taubes, and others).

At a theoretical level, I think a naturalist approach to religion is just asking questions I'm not interested in. They're perfectly legitimate in their own terms, but they don't address the actual experience of how one or other aspect of religion becomes existentially meaningful to us in our actual lives. The fact that we ourselves are the subject of investigation makes all the difference.

Ethics arises in the recognition of our obligation to care for others as beings, like us, exposed to mortality - that is, beings who need our help. Buddhism, not wrongly, extends this to 'all sentient beings'.

For others the mourning is over. Others would say that whilst one God has died - the God of ontotheology perhaps? - this allows for the good news of a God who is to come, a God who will be better able to gather up and give justice to all the manifold aspirations of human life towards goodness and meaning (and not just to those who are able to fit into a narrow 'religious' framework).

And this is also what he takes Christian doctrine, in all its complexity, to be centrally about, that is, teaching an attitude rather than a set of propositions. Call it joyous openness to life. What's not relevant about that?

But why should a religious person be interested in a work like Heidegger's that many regard as the epitome of nihilism? For a start, because Heidegger forces us in a way that few philosophers do to really think through the seriousness and all-encompassing nature of our mortality.

Now, as at the beginning of the 19th century, there is a certain discovery of Eckhart and related figures. There are questions as to how far our Eckhart accords with the real medieval teacher of that name, but there are certainly images in his work that help us work our way past several of the aporia with which we're confronted in our attempts to think about God.