The Sickness Unto Death

It is the inclination to accept that as far as the individual is concerned, death is indeed the end. Now why should Kierkegaard want to call that a sickness? After all, even in his own time there must have been people strong both in might and body who rejected the Christian teaching of sin and salvation, and who faced what they accepted as total extinction with equanimity. And today, of course, even in societies that once proudly professed Christian principles, the rejection of Christian belief--or at least the failure unequivocally to accept it--is the rule rather than the exception. So in what sense can the denial of Christian dogma constitute an illness?