Though it be a deep sorrow for sin that God requires as necessary to salvation, yet the very nature of it necessarily implies delight.  Repentance of sin is a sorrow arising from the sight of God’s excellency and mercy, but the apprehension of excellency or mercy must necessarily and unavoidably beget pleasure in the mind of the beholder…. how much soever of a paradox it may seem, it is true that repentance is a sweet sorrow, so that the more of this sorrow, the more pleasure.

Jonathan Edwards in John Piper, God Is the Gospel (Wheaton, IL: Crossway, 2005), 104.