What significant declaration was made during the Council of Chalcedon?

During the Council of Chalcedon, which convened in 451 AD, a significant declaration was made regarding the nature of Christ. The council articulated the belief that Jesus Christ exists in two natures: one fully divine and the other fully human. This doctrine is known as the Chalcedonian Definition, and it was crucial in the development of Christological understanding within Christianity. It aimed to address the debates and disputes regarding the nature of Christ that had arisen in earlier centuries, particularly in relation to the teachings of the various heresies that presented differing views on the relationship between Christ's divinity and humanity.

This declaration helped to clarify orthodox Christian belief and provided a framework for understanding how those two natures coexist within the one person of Jesus Christ. The Council of Chalcedon is therefore viewed as a defining moment in Christian theology, particularly in opposing monophysitism, which held that Christ had only a single, divine nature.

Other options, while relevant to broader theological discussions, do not pertain to the primary focus of the Council of Chalcedon. The supremacy of the Pope, the formation of the New Testament canon, and the condemnation of Arianism relate to different aspects of church authority, scripture, and heresy respectively,