Adam Clarke on Proverbs 12:25

Heaviness in the heart of a man maketh it stoop - Sorrow of heart, hopeless love, or a sense of God's displeasure - these prostrate the man, and he becomes a child before them.

But a good word maketh it glad - A single good or favorable word will remove despondency; and that word, "Son, be of good cheer, thy sins are forgiven thee," will instantly remove despair.