Sunday School Review: Basic Church History: Nicaea through the Middle Ages, Part 2

With last week's introduction (a fast-paced review of what we covered last spring) complete, let's dive into one of the most pivotal periods in church history—the rise of Constantine the Great and the events surrounding him that shaped the future of Christianity. From the Emperor’s surprising (and still questioned) conversion to the battle against Arianism and the Council of Nicaea, we will explore how God was at work during these transformative years.

If you’re new here and missed last week's review, you can find it here.

Constantine's Birth

Our story begins with Constantine, born around AD 272 to Constantius, a Roman officer, and Helena, his concubine and a devout Christian woman. His father would later become one of the rulers of the Roman Empire, and Constantine was raised in that political and military world.

As he rose through the ranks, Constantine’s ambition and strategic mind eventually positioned him as a contender for the title of emperor. In AD 312, at the Battle of the Milvian Bridge, Constantine’s life took a decisive and dramatic turn toward that end.

Constantine's Conversion

Before the battle, Constantine claimed to receive a vision. He allegedly saw a cross in the sky, accompanied by the words “In this sign, conquer.” That night, he reportedly had a dream where Christ instructed him to use the Christian symbol in battle. Constantine honored the vision, placing the Chi-Rho (the first two letters of “Christ” in Greek) on his soldiers’ shields. Miraculously, Constantine won the battle against overwhelming odds, and this victory set him on the path to eventually becoming the sole ruler of the Roman Empire.

There’s been much debate over the years about whether Constantine’s conversion was genuine. Some see it as politically motivated—an attempt to unify the empire by aligning with the growing Christian movement. However, several evidences suggest Constantine’s faith was sincere.

First, Constantine consistently favored Christians throughout his reign. His mother, Helena, was a sincere and devoted believer, and Constantine seemed to take her faith to heart. He built churches, gave Christians positions of influence, and ultimately proclaimed Christianity as the favored religion of the empire. The lavish extent of Constantine's favor seems beyond anything politically expedient.

In fact, his baptism, which took place near the end of his life, shows that he took the Christian faith seriously enough to want to die as a Christian. While it’s true that Constantine experienced some political benefit by embracing Christianity, the evidence points to a genuine belief in Christ and a desire to honor Him.

The Edict of Milan (313 AD)

In AD 313, a year after Constantine’s victory at the Milvian Bridge, he and his co-emperor, Licinius, issued the Edict of Milan. This was a groundbreaking moment in church history. For centuries, Christians had faced intense persecution, from Nero’s brutal executions to Diocletian’s widespread purges.

The Edict of Milan granted religious tolerance throughout the empire, effectively ending the persecution of Christians. Churches were returned, confiscated property was restored, and for the first time, Christians were free to worship openly without fear. The Edict didn’t just allow Christianity to survive—it set the stage for it to thrive.

Although the road to full religious freedom was gradual, the Edict of Milan marked a crucial turning point. Christians who had once been marginalized were now encouraged to step into public life, share their faith, and even serve in government positions. Eventually, Christianity would become the official religion of the empire, not just a tolerated one.

Arius and Arianism

However, as Constantine’s empire embraced Christianity, a theological crisis threatened the unity of the church. A presbyter and bishop named Arius from modern-day Libya was teaching that Christ, the Son of God, was not eternal but was instead a created being. Arius argued that Jesus, while divine in some sense, was not equal with God the Father. This teaching, known as Arianism, spread quickly, dividing believers.

The Council of Nicaea (325 AD)

Constantine, concerned about the division in the church and its potential impact on the stability of the empire, called for a church council in AD 325. His goal was to bring together Christian leaders from across the empire to settle the matter once and for all. This meeting became known as the Council of Nicaea.

This teaching struck at the heart of Christian doctrine. If Christ was not fully God, then the very nature of salvation was at risk. The early church had always taught that Jesus is both fully God and fully man, and only through His divinity could He bring salvation to humanity. But Arius’s ideas found many supporters, causing serious division within the church.

Athanasius

Enter Athanasius, a young deacon from Alexandria at the time of the Council of Nicaea, who would become one of the greatest defenders of orthodox Christian belief. Athanasius stood firmly against Arianism, arguing that if Christ were not fully God, then our salvation would be impossible. He championed the biblical truth that Jesus is co-eternal and co-equal with the Father—of the same essence or substance.

Athanasius’s bold defense of the full deity and eternality of Christ played a crucial role at the council. His clear articulation of the gospel helped to solidify the church’s stance on the matter, ensuring that the orthodox view of Christ’s full divinity would be upheld.

The Nicene Creed

After much debate, the Council of Nicaea came to a firm conclusion. The bishops overwhelmingly rejected Arius’s teachings, affirming that Jesus Christ is “begotten, not made,” and that He is of the same substance (Greek, homoousios) as the Father. This meant that Jesus is fully divine, co-eternal with the Father, and equal in power and glory with Him.

The council produced the first version of what we now call the Nicene Creed, a statement of faith that clearly affirms the full deity of Christ. The original version of the Nicene Creed states that Jesus is "the only-begotten Son of God, begotten of the Father before all worlds, Light of Light, very God of very God, begotten, not made, being of one substance with the Father."

This creed became a foundational declaration of Christian orthodoxy, uniting believers in their confession of the nature of Christ.

The Continuing Struggle with Arianism

Though the Council of Nicaea delivered a clear verdict, the battle against Arianism did not end there. Despite the council’s decision, Arianism continued to spread, particularly in the eastern part of the Roman Empire. Several emperors, including some of Constantine’s successors, were sympathetic to Arian beliefs, which allowed the heresy to persist for decades after the council.

Athanasius, who later became the bishop of Alexandria, spent much of his life defending the truth against Arianism. He was exiled multiple times for his steadfast refusal to compromise on the deity of Christ. It wasn’t until later church councils and the faithful perseverance of orthodox believers that Arianism was decisively condemned and faded into obscurity.

Conclusion

The events of Constantine’s reign and the Council of Nicaea remind us of God’s sovereignty over history. Even in the face of theological confusion and persecution, God preserved His church and ensured that the truth of Christ’s divinity would endure.

The Nicene Creed continues to be a testimony to the unity and strength of the Christian faith. As we look back at these pivotal moments, we’re reminded that the same Spirit who guided the early church continues to lead us today.

Thank you so much for joining us for this study of church history! If you found this helpful or encouraging, subscribe for more church history and theological content. Until next time, may God - Father, Son and Holy Spirit - bless you.

Grace and peace,

Kevin

Resources

Bruce L. Shelley, Church History in Plain Language (Nashville: Thomas Nelson, 1995).

Justo L. González, The Story of Christianity, Vol. 1: The Early Church to the Dawn of the Reformation (New York: HarperCollins, 1984).

Unless otherwise indicted, all Scripture quotations are from The ESV® Bible (The Holy Bible, English Standard Version®), © 2001 by Crossway, a publishing ministry of Good News Publishers. Used by permission. All rights reserved.