1. True godly sorrow is inward
It is inward in two ways:
(1) It is a sorrow of the heart. The sorrow of hypocrites lies in their faces: “they disfigure their faces” (Mat 6.16). They make a sour face, but their sorrow goes no further, like the dew that wets the leaf but does not soak to the root. Ahab’s repentance was an outward show. His garments were rent but not his spirit (1Kng 21.27). Godly sorrow goes deep, like a vein which bleeds inwardly. The heart bleeds for sin: “they were pricked in their heart” (Act 2.37). As the heart bears a primary part in sinning, so it must bear a primary part in sorrowing.
(2) It is a sorrow for heart-sins, the first outbreaks and stirrings of sin. Paul grieved for the law in his members (Rom 7.23). The true mourner weeps for the stirrings of pride and lust. He grieves for the “root of bitterness” even though it never blossoms into action. A wicked man may be troubled by scandalous sins; a real convert laments heart-sins.
-From Thomas Watson The Doctrine of Repentance (modernized by William Gross)