Heaney traces the hidden history of music's presence in Christian thought, including its often unrecognized influence on key figures such as von Balthasar, Barth and Bonhoeffer. She uses Lonergan's theological framework to explore musical composition as a theological act, showing why, when and how music is a useful symbolic form.

The book introduces eleven ground-breaking theologians, and each chapter offers an entry point into the thought of the theologian being presented through an original piece of music. Heaney argues that music is a universally important means of making sense of life with which theology needs to engage as a means of expression and of development. Musical composition is presented as an appropriate and even necessary form of doing theology in its quest to engage with the past, mediate truth to the present and tradition it into the future.