Simple Statement of the Trinity: There is one God who nevertheless exists in three persons: the Father, the Son, and the Holy Spirit, all of which share homoousios (Greek: “of one substance,” or “of one essence”) the same divine nature and are equal in power, glory, and Godhead.
Nestorius was an archbishop of Constantinople from 10th April 428 to 22nd June 431 A.D. It is not certain if Nestorius himself was a Nestorian; however, his name has been associated with this view. He got into trouble when he rejected the title, Theotokos – the idea that Virgin Mary should be called the “Mother of God”.
Regarding person and nature of Christ, Nestorius proposed two natures and two persons view. He believed that the unity of Christ’s human and divine natures is just like a man and his wife living under one roof. He believed that human and divine are impossible to unite with each other. If such union had occurred, then Christ could neither truly have been equal to God or consubstantial with God nor consubstantial with man, since God cannot be borne as a human, grow in to maturity, suffer, and die. However, there is a problem in this view. It makes difficult for Jesus to be both God and human at the same time. It diminishes the person and nature of Christ, thereby rejecting the true Logos Incarnation (In the beginning… [John 1:1,14]) in Nestorianism. Thus, Nestorius was condemned heretic by Cyril of Alexandria at the First Council of Ephesus in 431 A.D.
* Consubstantial (homoousios) : regarded as the same in substance or essence. This term homoousios stirred the Christendom which eventually led to Christological Controversy.