Most people who are not Christians think of physical death of our bodies as the only death and the only thing to be feared. But this death is what must happen to our bodies because of the way they are made. They cannot live for ever. Others believe that after your death you keep living as a spirit until you are forgotten by the living descendants.
But the Bible’s view of death is not physical. It is a spiritual death. When Adam and Eve disobeyed God, they died as God had warned them (Genesis 3:3). They were still alive physically, but they were already dead spiritually because their sin had separated them from God
(Ephesians 2:1; Isaiah 59:2).
All of us have inherited Adam’s nature so we are all in the state of the first death (spiritual death). But the wonderful news of the Gospel is that Jesus Christ came to die so that we could have life from this spiritual death. When we accept Jesus as our Saviour by confessing our sin and giving our lives to Him, we receive his new life (1 Corinthians 15:22). Even if our bodies die, our spirits will live with Him.
For those who do not believe or accept Him before their bodies die, there will be the second death. They are dead spiritually and if they do not receive forgiveness and therefore are not accepted by God, they will have the eternal punishment which is eternal separation from God. The Bible calls this the second death (Revelation 20:14 and 21:8).