Every tradition in Christianity has a way of describing the simultaneity of the spiritual life.
The Catholic/Orthodox traditions speak of the life of piety and mercy.
The Anglican/Wesleyan traditions speak of the life of personal and social holiness.
The Reformed tradition emphasizes a life of faith and works.
We are all describing the two great commandments and how they are realized in and through us. Spiritual formation thus becomes the shaping of the inner life in conformity to Christ and the sharing of the outer life with the compassion of Christ.
One is not to be played off against the other, any more than inhaling and exhaling can be pitted against each other.
As I have said before, this is why the fruit of the Spirit generates both inner character and outer conduct. The inner life of prayer becomes the outer life of service–all shaped and supported by community.
Nouwen has sought to write a book that keeps the inward and outward journies distinct but not separated. The early, midlife, and mature movements cultivate the personal and social dimensions. They produce a lifelong journey which shuns destinations in favor of ever-becoming.
In fact, Nouwen’s book is not an end in itself, but rather part of a trilogy–the next one being the importance of having good spiritual direction (vol. 2) that can generate discernment (vol. 3) for experiencing the spiritual formation (vol. 1) we have just explored. You may want to have all three volumes in order to view spiritual formation in this larger way.