Abraham Malherbe, Everett Ferguson, John Meyendorff

Eastern Orthodox Christianity, also known as Byzantine Christianity, stands as one of the primary divisions of Chalcedonian Christianity. It is structured around independent, self-governing churches, mirroring the ancient Pentarchy. Currently, there are seventeen recognized autocephalous churches, with others existing that lack mainstream acknowledgment. These churches elect their own leaders and can hold authority over other churches, some of which possess a greater degree of autonomy.

The faith's origins lie in the eastern Mediterranean, within the Byzantine Greek cultural sphere. Adherents share a common understanding and practices, viewing themselves as interconnected parts of a single church. A central theological tenet is the belief in the Trinity: one God existing in three distinct, co-equal persons—the Father, the Son, and the Holy Spirit—who share a single divine essence. They affirm that the Holy Spirit proceeds solely from the Father, rejecting the Filioque clause. Eastern Orthodoxy also posits a monotheistic God who is both transcendent and immanent, distinguishing between God's unknowable essence and his accessible, uncreated energies, a concept often referred to as Palamism.

Eastern Orthodox Christians adhere to a Trinitarian understanding of God, believing in three distinct, co-equal divine persons—the Father, the Son, and the Holy Spirit—who share a single, uncreated divine essence. The Father is considered unbegotten, the Son is eternally begotten of the Father, and the Holy Spirit eternally proceeds from the Father. This doctrine is summarized in the Nicene Creed, notably without the Filioque clause. Their monotheism acknowledges a God who is both transcendent and immanent. A key distinction is made between God's unknowable divine essence and his uncreated energies, through which God interacts with humanity. These energies are understood not as separate emanations but as God himself, distinct yet inseparable from his being, a concept often termed Palamism. The unity of the three persons in one essence is paramount, expressed through their shared divine actions, such as the salvation of humankind.

Within Eastern Orthodoxy, 'fallen nature' does not imply that human nature is inherently evil, but rather that it is susceptible to sin. Humans are created in God's image and are inclined towards sin, finding temptation attractive. Unlike some Western traditions, Eastern Orthodox Christians reject the idea that descendants are inherently guilty of Adam and Eve's original sin. Salvation is understood as a process of entering a new life through repentance and baptism, aiming to participate in the divine life through the Holy Spirit's work. This journey is a spiritual pilgrimage toward 'theosis,' or deification, where believers, while remaining human, become 'gods by grace' or 'icons of the living God.' This participation is in God's energies, not his essence, facilitated by God's gift of grace and the believer's cooperative acceptance.

The Eastern Orthodox Church views itself as the Body of Christ, encompassing all believers, living and departed, including saints, prophets, and even angels. This unity, known as the communion of saints, transcends time and space, uniting earthly and heavenly worshippers. The Virgin Mary, referred to as Theotokos ('Mother of God'), holds a preeminent position, seen as fulfilling Old Testament archetypes. Her role in conceiving Jesus, who is believed to be both fully God and fully human from conception, affirms Christ's divinity. Her perpetual virginity is also a tenet. The bodies and relics of saints are considered holy due to their participation in divine mysteries and their connection to God's work, often associated with miraculous occurrences. The Church rejects Purgatory, believing that after death, souls face a temporary judgment before the Final Judgment, where body and soul are reunited.