When the sun shines--the ice melts. When the Sun of righteousness once shines with beams of grace upon the soul--then it melts in mercy and tenderness.
Mercifulness is a melting disposition whereby we lay to heart the miseries of others, and are instrumental for their good. We must chiefly be merciful to the SOULS of others. Indeed soul-mercy is the chief of mercies.
That is a cruel mercy--when we see men go on in sin, and we let them alone. And that is a merciful cruelty--when we are sharp against men's sins and will not let them go to hell quietly.
Fond sentimentality is no better than cruelty. The surgeon cuts and lances the flesh—but it is in order to a cure. They are healing wounds. So when we lance men's consciences and let out the blood of sin, we exercise spiritual surgery. This is showing mercy.
"Rescue others by snatching them from the fire!" (Jude 23). If a man had fallen into the fire, though you hurt him a little in pulling him out--he would be thankful and take it as a kindness. Some men, when we tell them of sin say, 'O, you are unloving!' No! it is showing mercy.
If a man's house were on fire, and another should see it and not tell him of it, for fear of waking him--would not this be cruelty? When we see others sleeping in their sin, and the fire of God's wrath ready to burn them up--and we are silent--is not this cruelty?
(Thomas Watson, 1660, "The Beatitudes." Public Domain as seen on Grace Gems.)