2 Corinthians, chapter 7

When can sorrow be a good thing? When sorrow leads to repentance, which is different from regret, it can be a very good thing. First off, we need to look at the difference between repentance and regret. Regret means you feel bad about something. Repentance means you feel bad, but you do something about it and look to learn from the experience. True repentance brings about change in the heart instead of on the surface. Paul goes into detail about true repentance in 2 Corinthians 7 and the role that it plays in conjunction with Godly sorrow and worldly sorrow.

10Godly sorrow brings repentance that leads to salvation and leaves no regret, but worldly sorrow brings death. 11See what this godly sorrow has produced in you: what earnestness, what eagerness to clear yourselves, what indignation, what alarm, what longing, what concern, what readiness to see justice done. At every point you have proved yourselves to be innocent in this matter. 12So even though I wrote to you, it was not on account of the one who did the wrong or of the injured party, but rather that before God you could see for yourselves how devoted to us you are. – 2 Corinthians 7:10-12

Regret is something that can eat at a person. I know I struggle with the regret of a thousand decisions gone wrong. True repentance can erase this regret, however. As Paul describes here, true repentance causes us to strive not only for innoence, but to right any wrong that may have occurred. It causes us to strive for a cleanliness of spirit that can only be acheieved by the blood of Christ. Why do we do this? We do this out of devotion to Christ. It is almost done out of an effort to thank Him for the gift of salvation.