If we are seeking greater understanding in this area, the 51st Psalm is a good place to start. Through the words King David we are able to see a penitent heart. As most know this Psalm speaks of that moment after the prophet Nathan called King David to task for coercing Bathsheba to come to the palace and then building a mountain of sin through treachery, murder, betrayal, and deceit. Verse 17 causes us to hear an important Word as it says, "The sacrifice acceptable to God is a broken spirit; a broken and contrite heart, O God, You will not despise." The contrite heart is the penitent heart. It is what God desires for us to offer to Him in the aftermath of our sinful choices. Reading the story of David's many acts of deception and the prayer of his penitent heart provide for us help in understanding how to respond to this Lenten invitation to practice penitence.
As we read the Psalm, it becomes obvious that the penitent heart is painfully honest about what has been done against God. In our culture we make light of sin to the point that a casual and flippant, "Hey, I'm sorry about that God," seems like more than enough. Too many of our day have no idea about the seriousness of the sin which darkens our soul and separates us from the One who calls us to a life with Him. Without a serious attitude toward sin, penitence is an impossibility. With it, nothing is more important.