I Thess 4:13-5:11 The exact details of what will happen on Christ's return are not clear but what is clear is that those who died with their sins covered by His blood will celebrate his return and will live eternally with him.  As Christians, we grieve the death of a loved one - even Jesus grieved the death of Lazarus when he knew he would rise in a few moments- but we grieve with the hope that death is not the end.  Rather it is a door into something much greater for those who die in Christ.