Christians are not immune from the consequences of living in a fallen world and the effects of sin, death and satan. Indeed Jesus warned us we can expect trouble in this world. But he went on to say that he had overcome the world, and so we do not need to be afraid or to despair like those who have no hope.
Casualties Of Living In A Warzone
The trouble is that we live in a spiritual war zone between the First and Second Coming of Jesus Christ. [For more on this go to LIVING IN A SPIRITUAL WARZONE]
When Paul tells the Thessalonians they should not grieve like others who have no hope, he is not saying they should not grieve the death of a loved one. Jesus himself wept at the tomb of his friend Lazarus and over the state of Jerusalem and its refusal to heed his calls to repent before it was too late. So it is clear that grieving the death of a loved one is a normal - indeed necessary - part of our lives as Christians.
Christian Grief Is Different From The Grief Of People Who Have No Hope
Paul is saying that Christians should not grieve like the rest of the world that has no hope of resurrection and life after death.
If you have ever attended the funeral of someone who died without hope of eternal life, you may have witnessed the awfulness of the despair and grief that is often seen among the surviving relatives.
Contrast this with the scene at Christian services celebrating the life of a brother or sister in Christ, who has died and now sees Jesus face to face. In place of despair there is genuine sorrow at being separated by death from the loved one, but it is a sorrow tempered by the joy of knowing s/he is with Christ and that one day we shall be reunited for ever in heaven.