For the kind of sorrow God wants us to experience leads us away from sin and results in salvation. There’s no regret for that kind of sorrow. But worldly sorrow, which lacks repentance, results in spiritual death.
For the sorrow that is according to the will of God produces a repentance without regret, leading to salvation, but the sorrow of the world produces death.
And just as no human being comprehends any person’s innermost being except the person’s own spirit within him, so also no one comprehends what pertains to God except the Spirit of God.