Many Christians want to stop here and say that we will eventually receive glorified bodies, but that is all that we can know now. On this view we can say nothing more about whether our loved ones who have died are now conscious, living, or loving. But in fact this view is a tragic mistake, not least because it turns death into a very dark place and because it does not do justice to the particular character of our animality. We are rational animals. I talk about this in the book, and I can't go into it further here, but our animality is not the kind that simply is annihilated when we die.
The "demise of death" happens because of Jesus' Resurrection: only when we are united gloriously with God and each other in the final consummation, when we are present to Jesus and to each other in our glorified bodies, will death be fully conquered and the kingdom of God fully established. But we need to affirm also that death is not, for the Christian, what the materialist thinks it is. Death is not darkness, not annihilation, not loneliness. It is not this because we are spiritual animals, and our bodily death does not cut off our communion.
True, death brings our historical lives to an end, but we need to remember that God has made us spiritual animals: death does not obliterate us as it does other animals. If we aren't aware of this, and if we suppose that death annihilates us, then resurrection quickly begins to seem a very distant and quixotic hope: perhaps God will clone me at the end of time, but if so this new me would be merely a copy of me rather than being me! On this view death would win after all. The demise of death, therefore, must combine bodily resurrection and our ongoing life in God during the period (not a historical period, but a real waiting) between our bodily death and the consummation of all things.
Describe the beatific vision. Is this something that can really have an impact in modern life? How?
It is a simple thing, really. We are made for God, which is to say we are made for intimate personal communion in holiness. We are made for the joy and peace of charity and the adventure of wisdom. We are made to know Him as He is. Our earthly lives rightly entail many projects, but none of them fully fits us. The project that we want is actually to be known and loved by Him in such a way that we fully reciprocate that knowledge and love, so that we can really share in His life. Can God enable us to share in His life? Yes. And this is going to be an amazing thing. Jesus' risen body shows us, too, that our glorified bodies will be able to take part in the communion of charity or true friendship with the triune God—the communion that is what we mean when we talk about beatific vision.
What do you think happens after death for a believer? Do we have a spiritual soul, or is there a "sleep" experience?
If we were solely material beings, then we would not actually "sleep" at death. We'd simply be annihilated or become nothing. Obviously God could later reconstitute our bodies, but this reconstitution would be a copy rather than the real thing. When a material thing is destroyed, it can be rebuilt, but the newly built thing is not the old thing; it is a distinct, new material composite.
In fact, God made us not merely animals but rational animals. As I try to show in the book, the arguments that aim to show that we do not have souls are false both biblically and philosophically. N. T. Wright recognizes that the New Testament anticipates that death does not destroy us but instead a spiritual entity lives with God and awaits the resurrection of the body and the fullness of the new creation. This is what I think too. Although Wright polemicizes against Platonism, the spiritual soul really is not a merely Platonic doctrine. The key is this: death is a dreadful punishment, because we are body-soul unities; but death does not usher us into darkness, annihilation, or nothingness, even during the period prior to the final resurrection. Materialists accustom themselves to missing part of the picture, and this makes materialists (in general) more likely to have difficulty imagining bodily resurrection as a true fulfillment of the human "I."
What do you think of popular near-death experiences? Are they authentic? Colton Burpo's account in Heaven Is for Real, for example?
I've seen the book at the bookstore, but I don't know enough of the details. These experiences are authentic insofar as they make clear that death is not an entrance into gloomy non-being and non-relationality. Death is certainly a harrowing passage, but Jesus is with us, and so are many others in union of prayer. This seems to me to be the key point of near-death experiences. They also describe heaven in terms of communion or (on the contrary) of alienation. Their point again seems to be accurate: how we live now matters.