When I was an ardently practicing Lutheran (an era that concluded when I was about 20), my public formation was largely along the lines of right doctrine. A lot was made of adhering to a right set of beliefs and of learning these beliefs thoroughly.
Now as a Catholic I often feel that my public formation (by way of homilies) has a strong emphasis on right living. We need to do the right things, especially the right daily things such as prayer, service, faith sharing, and acts general goodness.
Both of these are necessary and good, or at least they are when one's conceptualization of rightness actually accords with truth.
But in both of these formulations, the most important Christian thing is missing: the how question. How am I supposed to live this way? How is it I am supposed to believe? How am I to interface with God? Not what do I do or what do I believe, but how do I do it?
How do I do it is, I think, the question of the heart of Christianity, because it hinges on lived experience, not on doctrine or moralizing. And the human heart is indeed key to the heart of Christianity. For one person to teach another how, one must have experienced heart change. (I do not deny that Jesus teaches coaches many people through to conversion interiorly through prayer, but I imagine that this is often a much longer process than being able to be directly discipled by another.)
And I believe that the key to the necessary heart change necessary to teach another is not mere intellectual enlightenment or moral exercise, but the encounter of my misery with God's mercy. Even more than that, our hearts need more than our own experience, we need the encounter with human misery in general. We need real experience with sin and degradation encountering the life-giving love of God. We need to know and experience God's forgiveness and healing for us and for others. This grants us a capacity for compassion. It allows us to realize that sin, suffering, degradation, and the need for God's merciful love is the universal human condition, regardless of what a person may present to our eyes.
The compassion capacity that opens in us is not only to give physical relief to suffering, though of course that is included. Even more it includes lifting souls from shame, shadows, and rejection into the light and solidarity and love of Christian community, of having belonging within the people of God.
Without this dimension, without being able to operate on this level of recognizing both within myself and within you our shared misery and our (at least potentially) shared experience of God's mercy, and addressing the reality, actually talking, teaching, and preaching about it, we are trapped in the intellect or in moralizing. Sharing experiences forms a bond. Human beings finding God's mercy need to rejoice with others who know this same joy or they will spiritually suffocate.
We need to be able to know, touch, courageously face, and articulate our realization of our misery, our utter need for God in every way. To do this, we need humility. We need time spent in silence so that we have the opportunity to meet ourselves. We need courage to face the truth we meet. We need the ability to be present also to another person and his suffering without trying to mute him when we dredges up what we'd rather not face in ourselves. We need frequent confession.
We also need penance and self-denial, but not the kind I do to impress myself with how much sacrifice I can bench press. We need penance that opens us to experiencing and accepting weakness. By this penance I intentionally touch my misery. And touching it, I turn in trust once again to God's infinite mercy and realize that that, and not my capacities, is what is awesome.