Patristic theology on the Holy Cross as the pillar of the Church’s unity is the central theme of this study, which analyses the teachings of the Holy Fathers — including Saint Maximus the Confessor, Saint Athanasius the Great, Saint Cyril of Alexandria and Father Dumitru Stăniloae — on the connection between the Sacrifice and the Resurrection of Christ the Saviour and ecclesial unity. The Cross, through its two arms, unites heaven with earth and man with his fellow human beings, whilst the Church is the place where the lost communion between God and man is restored, foreshadowing the perfect unity of the Kingdom of God.