The first Council of Nicea convened in Nicaea in Bithynia (present-day İznik in Turkey) by the Roman Emperor Constantine I on May the 20th, 1684 years ago...
The Council was historically significant as the first effort to attain consensus in the church through an assembly representing all of Christendom.
Historically significant as the first effort to attain consensus in the church through an assembly representing all of Christendom, the Council was the first occasion for the development of technical Christology. Through it a precedent was set for subsequent general councils to adopt creeds and canons. This council is generally considered the beginning of the period of the First seven Ecumenical Councils in the History of Christianity.
The agenda of the synod were:
1)The Arian question regarding the relationship between God the Father and Jesus; i.e. are the Father and Son one in purpose only or also one in being;
2)The date of celebration of the Paschal/Easter observation
3)The Meletian schism;
4)The validity of baptism by heretics;
5)The status of the lapsed in the persecution under Licinius.
Finally, the council promulgated twenty new church laws, called canons, (though the exact number is subject to debate), that is, unchanging rules of discipline. The twenty as listed in the Nicene and Post-Nicene Fathers are as follows:
1. prohibition of self-castration; (see Origen)
2. establishment of a minimum term for catechumen;
3. prohibition of the presence in the house of a cleric of a younger woman who might bring him under suspicion;
4. ordination of a bishop in the presence of at least three provincial bishops and confirmation by the metropolitan;
5. provision for two provincial synods to be held annually;
6. exceptional authority acknowledged for the patriarchs of Alexandria and Rome, for their respective regions;
7. recognition of the honorary rights of the see of Jerusalem;
8. provision for agreement with the Novatianists;
9–14. provision for mild procedure against the lapsed during the persecution under Licinius;
15–16. prohibition of the removal of priests;
17. prohibition of usury among the clergy;
18. precedence of bishops and presbyters before deacons in receiving Holy Communion, the Eucharist;
19. declaration of the invalidity of baptism by Paulian heretics;
20. prohibition of kneeling during the liturgy, on Sundays and in the fifty days of Eastertide ("the pentecost"). Standing was the normative posture for prayer at this time, as it still is among the Eastern Orthodox and Eastern Catholics. (In time, Western Christianity adopted the term Pentecost to refer to the last Sunday of Eastertide, the fiftieth day.)
On July 25, 325, in conclusion, the fathers of the council celebrated the emperor's twentieth anniversary. In his valedictory address, Constantine again informed his hearers how averse he was to dogmatic controversy; he wanted the Church to live in harmony and peace. In a circular letter, he announced the accomplished unity of practice by the whole Church in the date of the celebration of Christian Passover (now called Easter).
The long-term effects of the Council of Nicaea were significant. For the first time, representatives of many of the bishops of the Church convened to agree on a doctrinal statement. Also for the first time, the Emperor played a role, by calling together the bishops under his authority, and using the power of the state to give the Council's orders effect.
In the short-term, however, the council did not completely solve the problems it was convened to discuss and a period of conflict and upheaval continued for some time. Constantine himself was succeeded by two Arian Emperors in the Eastern Empire: his son, Constantine II and Valens. Valens could not resolve the outstanding ecclesiastical issues, and unsuccessfully confronted St. Basil over the Nicene Creed.
Pagan powers within the Empire sought to maintain and at times re-establish Paganism into the seat of Emperor (see Arbogast and Julian the Apostate). Arians and the Meletians soon regained nearly all of the rights they had lost, and consequently, Arianism continued to spread and to cause division in the Church during the remainder of the fourth century. Almost immediately, Eusebius of Nicomedia, an Arian bishop and cousin to Constantine I, used his influence at court to sway Constantine's favor from the orthodox Nicene bishops to the Arians. Eustathius of Antioch was deposed and exiled in 330. Athanasius, who had succeeded Alexander as Bishop of Alexandria, was deposed by the First Synod of Tyre in 335 and Marcellus of Ancyra followed him in 336. Arius himself returned to Constantinople to be readmitted into the Church, but died shortly before he could be received. Constantine died the next year, after finally receiving baptism from Arian Bishop Eusebius of Nicomedia, and "with his passing the first round in the battle after the Council of Nicaea was ended."