The Grand Unified Theory in Theology encapsulates the entirety of Metropolitan John Zizioulas's theological perspectives within a singular, comprehensive framework. In his approach, Zizioulas presents a holistic Christian theology, emphasizing the profound impact of eschatological ontology on all aspects of Christian doctrine.

As a Systematic Theology approach to answering the questions of reality—faith, science, art, mysteries of life, death, time, freedom, and love—Zizioulas’ Theory of Everything in Theology sets the results of other human inquiries in light of the relational ontology of the Bible and the Greek neo-patristic synthesis. With this Methodology, the fundamental aspects of theology are present in the liturgical Tradition as the Church Fathers conceived them and as they are lived constantly by the Church through its Eucharist and Ascetical Ethos.

While Zizioulas insists on the Trinitarian Doctrine of Persons in Communion as the center point or source of the whole theological system, he managed to incorporate within it essential elements not only anthropology, Christology, and Pneumatology (Holy Spirit), Eschatology, but also Ecclesiology, Cosmology, and Ecology, demonstrating its relevance for Philosophy & Ontology. All of this is shown in the Analysis of the Opus.

According to Fr. John Meyendorff, "The voice of John Zizioulas may turn out to be the fresh voice for which theology and especially ecclesiology have long been waiting. In the context of a complete theology, which includes extended consideration of the major theological topics—the Trinity, Christology, eschatology, ministry and sacrament, but above all, the eucharist—the author propounds a fresh understanding, based in the early Fathers and the Orthodox tradition, of the concept of person, and so of the Church itself."