No one else can give us this assurance. Mourning that comes from sorrow of our own sins. Nearly all the commentaries on this text point out that the context applies also to those who have lost their innocence, their righteousness, their self-respect, not just their loved ones. Jesus points us not only to the sorrow of bereavement but also to the sorrow of repentance . It is one thing to know we are lost and empty without God, it is another to grieve over it.
Confession is one thing, contrition is quite another.
I realize this attention to our sin is jarring to the spirit of our world that has turned to a wild pursuit of happiness. Many will bemoan any attention in the Christian world that points to our sins. I recall my good friend Bruce Larson telling about a halfway house for juvenile delinquents, I think it was in Canada. This home was created as a way to help young boys make the transition back into the world after being in trouble with the law and spending time in prison. Wellness begins with facing our sin and grieving over our sins.