I understand that there is no birth and no death in this phenomenal world according to the law of conservation of energy and mass. Our body can't become nothing. It just changes its form and will continue eternally.
The law of conservation of energy and mass is already scientifically proved. Death is just a notion which means the end of manifestation of our present body. Even if our present body disintegrates, it continues to exist eternally by changing its form as water, minerals, heat...etc.
Thay says, "Even a cloud can never die. How can we die?"
(... ⇒ vapor ⇒ cloud ⇒ rain, snow ⇒ ocean, land ⇒ vapor ⇒ cloud ⇒ ...) Humans named "vapor ⇒ cloud" as the birth of a cloud or the death of a vapor. And we named "cloud ⇒ rain, snow" as the death of a cloud or the birth of rain or snow. But they just keep existing as water eternally.
In case of humans, a cloud can be liken to a body and water can be liken to the whole cosmos. If we use notions of birth and death, our body needs to be born and die. However, if we understand that we are the whole cosmos, we don't need to be born or die. The ultimate truth is no birth and no death, so we don't have to use the notions of birth and death. We have been the whole cosmos since the non-beginning and will be the whole cosmos till non-end, or eternally. So, we don't have to be afraid of death anymore.