Celtic Studies is an interdisciplinary academic field that explores the languages, history, culture, politics, art, and belief systems of the Celtic-speaking peoples from antiquity through the modern era.

The field examines the rich Celtic cultural and philosophical traditions that shaped much of Western European heritage. Celtic studies investigates themes such as mythological cycles, medieval literature, heroic traditions, and sacred relationships with nature—core elements of the Celtic worldview.

Scholars also focus on the social and metaphysical dimensions of Celtic spirituality, including pre-Christian spirituality, Druidry, and the evolution to Christianity that began in the early post-Roman period.

Gregory has studied extensively on Celtic culture, religion, and spirituality, focusing especially on Celtic Christianity during the early medieval period. In particular, Gregory focuses on the enduring Celtic sensibilities—nature reverence, hospitality, community life, and theological systems that center around existential meaning instead of abstract dogma.

He also examines the modern expressions of Celtic identity, exploring the intersection of culture, politics, and religion in contemporary Ireland. His work highlights how the enduring Celtic worldview continues to offer wisdom and depth to today’s discussions around faith, identity, and meaning in the Western world.​