Feelings of sorrow alone aren't necessarily conviction. We can be sorrowful for many reasons, including selfish ones. We can be sorry for the bad consequences of our sin, sorry we were caught, sorry we lost someone's respect. The kind of worldly grief can't begin to address the true offense of sin, and it can't begin to change us [see 2 Cor. 7:8-9]. Only godly grief brings repentance. And only repentance testifies to the surgical effect of God's truth applied to our sinful hearts.