Blessed are they that mourn: for they shall be comforted. (Matthew 5:4)
By the valley of weeping we come to Zion. One would have thought mourning and being blessed were in opposition, but the infinitely wise Savior puts them together in this Beatitude. What He has joined together let no man put asunder. Mourning for sin—our own sins, and the sins of others—is the Lord’s seal set upon His faithful ones. When the Spirit of grace is poured upon the house of David, or any other house, they shall mourn. By holy mourning we receive the best of our blessings, even as the rarest commodities come to us by water. Not only shall the mourner be blessed at some future day, but Christ pronounces him blessed even now.
The Holy Spirit will surely comfort those hearts which mourn for sin. They shall be comforted by the application of the blood of Jesus and by the cleansing power of the Holy Ghost. They shall be comforted as to the abounding sin of their city and of their age by the assurance that God will glorify Himself, however much men may rebel against Him. They shall be comforted with the expectation that they shall be wholly freed from sin before long and shall soon be taken up to dwell forever in the glorious presence of their Lord.
C.H. Spurgeon, Faith’s Checkbook