The Bible teaches that God created us to be His image-bearers, which makes us distinct from the entire rest of creation. But when Adam and Eve chose to rebel in disobedience, their fall into sin distorted and marred the sacred Image. It makes sense that this biblical view of human nature reveals the reasons why mankind is capable of producing both Mother Teresa and the holocaust. In the movie Flatliners, medical students took turns stopping each other's hearts to give them a chance to experience what happens after death. After a few minutes, they resuscitated the metaphysical traveller who told the others what he or she saw.
Mankind deserves an answer.
Now it's up to the physical sciences. Well, maybe religion failed, but the Lord Jesus didn't. But first, let's address how naturalism answers this question. Because this world view says that there is nothing outside of space, time and energy, naturalism insists that death brings the extinction of personality and the disorganization of matter. Things just stop living and start decomposing.