The second group referenced by Jesus at the opening of the Sermon on the Mount are “those who mourn.” Just as Jesus taught that the poor in spirit would attain the kingdom of heaven, the mournful will be comforted.
The mournful — in the context of the Beatitudes — is not about people who have suffered loss. The comfort Jesus speaks of is for those who express sorrow for their sins and repent. The forgiveness of sin and the promise of eternal salvation is the comfort that Jesus offers to the mournful sinner.
MATTHEW 5: 4
4 Blessed are they that mourn: for they shall be comforted.