Our life on earth is just temporary. Everyone born will die one day. Jesus had come initially to pay the price for our sins and to show us the way to heaven. He is now in Heaven. He promised to come back. When Jesus comes back he will take all those trust in Him to be with Him forever. We call that Heaven. All those who died before he comes back, but had put their faith in Jesus as the only Lord God and Savoir of their life will go to Heaven. But those who are alive when he comes again, will be transformed and will go with Him.  This second coming of Jesus can happen anytime.