Blessed are they that mourn: for they shall be comforted.
Matthew 5:4 NIV
To mourn is to feel or show grief or deep sorrow or regret. However, you may want to ask: “is Jesus now calling us to always grieve or be sorrowful so that we too can partake in this blessedness?”. But it is not so in the literal sense. As the poorness that is qualified for a blessing is that of the spirit (v3), so also, is the mourning. It is that which its origin is spiritual and made manifest in the physical. Meanwhile, let us consider this scripture from the Amplified Version to gain more insight:
Blessed [forgiven, refreshed by God’s grace] are those who mourn [over their sins and repent], for they will be comforted [when the burden of sin is lifted].
Matthew 5:4 AMP
Spiritual mourning is not the mourning of a melancholy disposition. No, it is not sorrow over temporal distress, sorrow in adversity, sorrow because of a loss or disappointed hopes. But it is deep sorrow or grief over sin, such that is birth from a sense of poorness in spirit. Spiritual mourning is the mourning that leads a sinner to repentance. It is sorrow over the imperfect and afflicted state of the Church.
Indeed, what a great blessing shall be of the spiritual mourners, for they shall be comforted here in this age, by the God of all comfort, by Christ the comforter; by the Spirit of God (The Comforter); by the Scriptures of truth; by the promises of the Gospel; and by the ministers of the word, who have a commission from the Lord to speak comfortably to them.
Then are they comforted, when they have the discoveries of the love of God, manifestations of pardoning grace, through the blood of Christ, and enjoy the divine presence: and they shall be comforted hereafter; when freed from all the troubles of this life, they shall be blessed with uninterrupted communion with Father, Son, and Spirit, and with the happy society of angels and glorified saints.