The Council of Nicaea was convened in 325 CE to debate issues surrounding Christianity. By this time, the nascent religion of Christianity had spread throughout the Roman world. Emperor Constantine converted to Christianity and, in doing so, made it inevitable that the religion would soon become the official religion of the Roman Empire. The Council of Nicaea was convened to debate theological issues, such as the nature of Christ’s divinity.

The Council of Nicaea was convened on the orders of Constantine I in 325 CE. The purpose of the Council of Nicaea was to debate various theological issues, such as the true nature of Christ’s divinity.

The Nicene Creed was established by the Council of Nicaea in 325 CE. The Council of Nicaea was the first ecunemnical council in the history of Christianity (there have since been countless). It was convened to debate issues of Christ’s divinity and to ensure universal agreement among the divergent theological schools of thought. The Nicene Creed is a profession of faith that states that Christ is the Son of God, that he descended from heaven to save us, and that he died to absolve our sins.

The persecution of Christians in the Roman Empire arguably began with the execution of Christ and certainly was commonplace throughout the first and second centuries. The height of Roman persecution of Christians, however, was not reached until early in the fourth century, during the reign of Diocletian. The so-called Diocletianic Persecution began in 303 CE, with an edict issued by the rulers of the Tetrarchy stating that all Christians had to conform to Roman worship on penalty of death. Many Christians were executed in brutal circumstances during this time, yet it was just a decade later that Constantine issued his Edict of Milan providing for religious tolerance of Christians in the Roman Empire.

The Battle of Milvian Bridge was fought in 312 CE, between rival forces in the Roman Empire. According to primary sources, Constantine had a dream in which God visited him and instructed him to fly the Christian cross as his standard. Constantine, who won the battle, felt like this was divine intervention and enthusiastically embraced Christianity throughout the remainder of his life.

Theodosius was the first instill Christianity as the official religion after Constantine I had introduced it to the people of the Roman Empire. This question is all about time frame. If we remember that Constantine brought religion to Rome, then we also know that Theodosius I was the first ruler after to make it official. It would be tricky to confuse which Theodosius claimed the official religion. The other two options were no where near Constantine's rule of Rome.

Emperor Constantine I (also called Constantine the Great) supposedly had a vision during the Battle of Milvan Bridge in 312 CE in which he saw a cross of light hovering above the battlefield along with the words "in this sign, conquer".

The following year, the Edict of Milan granted tolerance to all religions, including Christianity. Christianity would later go on to become the state religion of the Roman Empire in 380 CE.

The First Council of Nicaea was convened by Emperor Constantine I in 325 CE. The main purpose of this council was to debate the nature of Jesus Christ in relation to his divinity according to Scripture.

The council concluded that Jesus Christ was divine, co-eternal with God the Father as according to Christian doctrine.

The Edict of Milan was issued in 313 CE by the Emperor Constantine (and the Western Roman Emperor Licinius). It formally ended the policy of religious persecution of Christians in the Roman Empire. It also established the official state tolerance of Christian worship, leading to Christianity later becoming the official religion of the Roman Empire during the reign of Theodosius I.

The First Council of Nicea (325 AD) created the Nicene creed as a way to unify the fragmenting and diversifying beliefs in Christianity developing throughout the Byzantine empire. It establishes and explains the relationships between God, Jesus Christ, and the Holy Ghost. The other answers are incorrect because it was not crafted as legislation for political purposes, and was written to counter Arian Christianity, which questioned elements of the orthodox faith.