It would be interesting to look historically at the question, when did the idea that we need to do Penance fall out of our mindset?
The first reading and the gospel today deal with how the people of Nineveh responded to the preaching of Jonah and according to the custom of the time put on sack cloth and ashes. No, I am suggesting we need to do that but I do think we need to find our modern equivalent.
Humans are physical beings, and as such we are beings not simply of thought but of action. As a matter of fact we know that sometimes the action needs to precede the thought. We feel tired. We don't feel like exercising. The best response is to get up and move anyway and sure enough over time we have more energy and we feel less tired and more like exercising.
Doing penance it seems to me must start with the acknowledgement of sin. We need to stop rationalizing our behavior and name the sins.
We need to recognize that there two aspects to the effect of sin: the guilt and the penalty.
Forgiveness relieves us of the guilt, but in justice there is still a penalty. I may apologize for running into your car, and you may accept my apology, but I still, in justice, owe you for the repair. God is like a good parent; being forgiven does not mean that there is no punishment. God is merciful but also just.
Fasting as a penance, is not about the health benefits. Alms-giving done as penance is not about helping the poor( we should do that year round).
Our acts of penance done during Lent is about paying the penalty for the sins we commit. Part of the good news of the Christian faith is that we believe that while we are alive God gives us the chance to choose the penance. We can pick our punishment, if you will.
The much maligned concept of the plenary indulgence is the perfect balance of justice and mercy. Most are very simple actions. We believe that if done with a spirit of true contrition, because of the super-abundance of God's mercy bring full remission of temporal punishment due to sin.( the penalty)
So in recent years have so emphasized the mercy of God that they have all but obliterated the justice. Once again we must seek balance.
This Year of Faith the Holy Father has designated several special plenary indulgences, perhaps this Lent would be a good time.
The simplest and most common plenary indulgence is attached to the praying the Stations of the Cross. Even walking them individually, and mediating on each station, combined with the usual three conditions: confession, communion, and prayer for the Holy Father fulfills the requirement.
Indulgence is a gift from God that should not be dismissed.