In 1 Thessalonians 4:13, believers should not grieve over the dead like the rest, who are without what?

Answer: Hope

Paul writes so they will not grieve like the rest, who are without hope, since God will bring with Jesus those who have fallen asleep.

“Brothers, we do not want you to be uninformed about those who sleep in death, so that you will not grieve like the rest, who are without hope. For since we believe that Jesus died and rose again, we also believe that God will bring with Jesus those who have fallen asleep in Him.”— 1 Thessalonians 4:13-14 (BSB)