In Christianus, Abbot Vonier presents an absorbing theological reflection on how the indwelling of Christ expresses itself in the Christian moral life, in the visible "form of the Christian Person." Through a series of meditations on the distinct components of Catholic morality and spirituality-discipleship, prayer, liturgy, fruitfulness, temptation, citizenship, preparation for death-Vonier offers a view of how the whole Christian person is formed, from the center out, by the charity of Christ.

Both personally inspiring and theologically exact, Vonier's reflections lead the reader to a distinctly Christ-centered view of the truly happy life. He insists that to experience joy in the practice of virtue, "We must, above all things, become wise in the mysteries of Christ's personality."