Well, the Christian doctrine of the afterlife is simply integral to Christian doctrine, period, and indeed, the faith as a whole makes no sense if the life to come is ignored or trivialized. The heart of the Christian faith is the incarnation, death and resurrection of Christ, which provides salvation and redemption for God’s whole fallen creation.
I believe these Christian doctrines of the afterlife provide powerful resources to make sense of some of the perennial big questions like the problem of evil, the foundations of morality, and the very meaning of life. And again, insofar as we think Christianity is true because it makes sense of things, we also have reason to think the doctrines of the afterlife are true, since they are integral to Christianity.