Blessed are those who mourn, for they shall be comforted. This would be as confusing to crowds today as it was to the audiences of that time. Jesus addressed both worldly and spiritual mourning.
Worldly mourners experience sadness for a material or personal loss.
Their comfort enters when they give up their rights to whatever it is they mourn, and seek Jesus Christ as their source of comfort. Spiritual mourning comes from a heart that is sick from knowledge of its own sinfulness. He has words for those who do not recognize their deep need and refuse to repent. Some try to change the terms for salvation, insisting that they can save themselves or that they don't need saving at all. Each Christian has walked down the road of repentance leading to salvation.