Which council primarily addressed the nature of Christ and the Trinity?

The Council of Nicaea, held in 325 AD, is primarily recognized for addressing critical theological issues concerning the nature of Christ and the relationship within the Trinity. This council was convened by Emperor Constantine to resolve the Arian controversy, which questioned the divinity of Jesus Christ. The council concluded that Jesus is consubstantial (of the same substance) with the Father, thus affirming the doctrine of the Trinity as a foundational belief of Christianity.

The Nicene Creed, established during this council, articulated the Church’s belief in the divinity of Christ, explicitly stating that he is “true God from true God.” This clarified the understanding of Christ’s nature in relation to God the Father and laid the groundwork for subsequent discussions about the Trinity.

While other councils also dealt with related topics—such as the Council of Chalcedon in 451 AD, which focused more on the two natures of Christ (divine and human), and the Council of Constantinople in 381 AD, which expanded on the Nicene Creed—Nicaea is specifically recognized for its foundational role in defining the relationship within the Trinity and affirming Christ's divinity.