William Burkitt on Matthew 5:4

Observe here, 1. That mourning for sin is a gospel-duty: the law allows no place for repentance, though we seek it carefully with tears.

Observe, 2. The time and reason for this duty. Blessed are they that now mourn. Sorrow for sin is physic on earth, but it is food in hell. Repentance is here a grace, but there a punishment.

Observe, 3. As mourning goes before comfort, so comfort shall follow after mourning. Our godly sorrow for our own and others' sins shall end in everlasting joy and comfort.