The video discusses two important ecumenical councils in early Christianity: the Council of Nicaea in 325 CE and the Council of Chalcedon in 451 CE. The Council of Nicaea spoke about the essence of the Christian faith and the doctrine of the Trinity. It proclaimed that there is one God the Father, one Lord Jesus Christ who is the only begotten Son of God, and the Holy Ghost, and that these three are one. The later Council of Chalcedon dealt with the question of the nature of Jesus Christ and sought to reconcile his divinity and humanity. It aimed to explain his divinity. Both councils helped address controversial theological issues in early Christianity through these important rulings and formulations of doctrine.