Trinity Sunday marks the beginning of ordinary time in the Church Calendar. During this season between Pentecost and Advent, we dial our liturgical lenses out for a wide-angle perspective on the journey of faith. This first Sunday of the season calls us back to the principal mystery of faith, to the Holy Trinity in whom we live, move, and have our being.

More than ever, evangelicals need to own the faith we claim to believe. As we venture into the future of a post-Christian West, fuzzy views of God abound without and within the church. Outside, our world offers a buffet pantheon with gods galore. The high god preached by our culture’s prophets and priestesses is an amorphous deity molded by the spirit of the age. This “god” has no definitive shape, no moral absolutes, and no holy wrath toward sin. It accommodates all creeds and lifestyles, and excludes no one from paradise. Then there’s the easily comprehended monad of Islam and the Jehovah’s Witnesses, along with the procreating gods of Mormonism. Within the visible church, large swaths of Pentecostals embrace sub-Trinitarian views, while rogue “evangelicals” like Rob Bell preach neo-Liberal Arianism. In the midst of all this theological confusion, Trinity Sunday calls us to know our God.

Approaching the Trinity requires a life posture of prayer and contemplation, a pilgrimage into deeper understanding and transformative worship. Think of the following sources as guides toward that end. Here you will find both classical and contemporary voices, ranging from entry-level to advanced reflection. Start where you are and begin the journey!

Larry W. Hurtado’s God in New Testament Theology claims logical priority. His small book is not about the Trinity per se, but by outlining the triadic shape of God in the NT, it shows indirectly how the Church’s subsequent articulation springs organically from the Scriptures. Saint Augustine’s On Christian Belief published by New City Press offers a classic intro to the Church’s faith. Within that volume his comments on the Trinity appear in Faith and the Creed, 165-71 and the Enchiridion on Faith, Hope, and Charity, 277-78, 297-302. The best entry discussions from contemporary thinkers include Donald Fairbairn’s Life in the Trinity, Fred Sanders’ the Deep Things of God, 2^nd edition, and my personal favorite The Incarnation of God by John Clark and Marcus Johnson. I also commend Edith Humphrey’s rich Trinitarian Spirituality in her Ecstasy and Intimacy: When the Holy Spirit Meets the Human Spirit.

Other sources offer intermediate to advanced discussions. Especially rich treatments appear in Thomas C. Oden’s Classic Christianity: A Systematic Theology and Robert Letham’s The Holy Trinity: In Scripture, History, Theology, and Worship. Also, Fred Sanders’ The Triune God is short but erudite, offering a fresh engagement with a wide range of issues in Trinitarian Theology. I highly recommend Thomas F. Torrance’s The Trinitarian Faith: the Evangelical Faith of the Ancient Catholic Church, 2^nd edition. In my opinion, Torrance’s The Christian Doctrine of God: One Being Three Persons is among the Church’s greatest reflections. John Owen’s Communion with the Triune God, now helpfully edited by Kapic and Taylor, is one of the more profound books of Christian spirituality.

If you’re interested in thinking with the Church about the Trinity through time, J. N. D. Kelly’s Early Christian Doctrines and Jaroslav Pelikan’s multi-volume The Christian Tradition, remain helpful. After the general orientation these books provide it’s always better and more enjoyable to engage the primary sources. The Popular Patristics series offers three  volumes in Trinitarian thought worth noting: Athanasius’s On the Incarnation, and his letters to Serapion in Works on the Spirit, along with Gregory of Nazianzus’s On God and Christ. Augustine’s De Trinitate represents the pentacle of early Church reflection. His book is not for the faint of heart, but Edmond Hill’s notes in the New City Press edition provide stellar guidance. You can find the medieval perspective under Question 31 in Thomas Aquinas’s Summa Theologiae. Finally, for the musings of the superstar theologian of the Reformation you can read John Calvin’s institutes of the Christian Religion, Book I. XIII. Now all that’s left to do is heed the voices summoning Augustine so long ago, tolle lege, take and read!