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.

Introduction

We cannot fully appreciate the transformative reign of Constantine without understanding the rich history that preceded it. The first three centuries of Christianity were marked by significant doctrinal development, organizational adaptation, and intellectual defense, all set against a backdrop of persecution and cultural opposition. As such, we took some time to discuss these dynamics.

The Apostolic Fathers

The Apostolic Fathers were early Christian leaders directly connected to the apostles, serving as crucial links to their teachings. For instance, Ignatius of Antioch, en route to his martyrdom under Emperor Trajan, wrote seven letters appealing to apostolic teaching and urging the churches to maintain unity and resist heresies like Docetism, which denied Christ’s true humanity. Moreover, Polycarp of Smyrna, a disciple of John the Apostle, embodied the steadfast faith of the apostles in his own martyrdom, famously declaring, “Eighty and six years I have served Him, and He has done me no wrong.” Finally, Clement of Rome’s letter to the Corinthians defended apostolic authority, addressing disputes over church leadership and reminding believers of God’s orderliness in creation.

The Apologists

By the second century, the church faced increasing scrutiny from the Roman Empire and Greco-Roman intellectuals. Christian defenders known as apologists emerged to advance the faith with reason and Scripture. Justin Martyr, a former philosopher, presented Christianity as the true “logos,” fulfilling the highest ideals of philosophy, in works like First Apology. Athenagoras’s A Plea for the Christians refuted accusations of atheism and immorality, emphasizing Christian worship of the one true God. Tertullian’s writings, including Apology, challenged Roman persecution, boldly declaring, “The blood of the martyrs is the seed of the Church.” Their efforts not only aimed at persuading outsiders but also at strengthening the faithful amid cultural hostility. By God's grace, they succeeded in many respects.

Early Heresies

The early church encountered significant theological challenges, including errant beliefs like Gnosticism, Marcionism, and Montanism. Gnosticism, a syncretic movement, taught that salvation came through secret knowledge (gnosis) and viewed the material world as evil, contrasting sharply with Christianity’s teaching of creation’s goodness and the total lordship of Jesus Christ over the visible and invisible (Colossians 1:15-21). Moreover, Marcion, a wealthy shipowner, rejected the Old Testament and its God, advocating a truncated canon that excluded anything he deemed “Jewish.” His views spurred the church to formally recognize the broader New Testament canon. Finally, Montanism, led by Montanus and two prophetesses, emphasized direct revelations from the Spirit and apocalyptic fervor, often in opposition to established church authority. Each heresy prompted the church to clarify doctrine and safeguard the apostolic faith.

The Church Fathers

Responding to these challenges, gifted theologians like Irenaeus, Tertullian, Clement of Alexandria, and Origen articulated and defended orthodox Christianity. Irenaeus’s Against Heresies dismantled Gnostic beliefs, emphasizing the unity of Scripture and the redemptive plan of God from creation to Christ. Tertullian, known for coining terms like Trinity and substance, provided a linguistic framework for theological discourse, although his later association with Montanism clouded his legacy. Clement, bridging Christian faith and Greek philosophy, encouraged believers to pursue knowledge and virtue in harmony with divine revelation. Origen, one of the most prolific early theologians, developed systematic theology in works like On First Principles, though some of his speculative ideas sparked later controversy. While a full consideration of their works rests outside the scope of this class, we must note the necessity and worthiness of their efforts.

The Apostles’ Creed

In this period, the Apostles’ Creed emerged as a concise summary of Christian belief, rooted in baptismal confessions. Its affirmations of the Trinity, Christ’s incarnation, death, and resurrection countered heretical distortions and unified diverse Christian communities. Phrases like “conceived by the Holy Spirit, born of the Virgin Mary” directly confronted Docetism, while “descended into hell” [or into the grave] highlighted Christ’s victory over death. The creed became and remains an indispensable tool for catechesis and liturgical use.

The Development of Episcopacy

As the church grew, its organizational structure evolved. Initially, leadership centered on a plurality of elders (presbyters), as seen in New Testament texts like Acts 14:23 and Titus 1:5. However, by the late first and early second centuries, bishops began to assume greater authority as defenders of doctrine and unity. Ignatius of Antioch’s letters highlight this development, urging churches to follow their bishops as Christ’s representatives. This transition to a monarchical episcopacy provided stability, particularly during times of persecution and doctrinal disputes, but also marked a significant shift from earlier practices and occasioned other significant departures from biblical practice. We will return to this consideration later in our study.

Context for Constantine

These formative centuries established a foundation of theological depth, organizational resilience, and spiritual courage. As Constantine ascended to power, he inherited a church shaped by these trials and triumphs—a church ready to influence the empire but still grappling with internal and external challenges. Understanding these early developments illuminates the profound impact of Constantine’s reign and the church’s enduring mission to proclaim the gospel.

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.

Questions for Review

1. Constantine's conversion has been debated for centuries. What do you think about the evidence of his faith—was it sincere or politically motivated? How does his story challenge or inspire your own understanding of public faith?
2. The Edict of Milan marked a dramatic shift from persecution to acceptance for Christians. What are the potential blessings and challenges of moving from being an oppressed minority to holding cultural influence? How might this relate to the church's position in society today?
3. The theological battle over Arianism centered on the nature of Christ. Why is it vital to affirm that Jesus is both fully God and fully man? How does this doctrine shape our understanding of salvation and worship?
4. Athanasius faced intense opposition in his defense of Christ's divinity, even enduring exile multiple times. How does his perseverance encourage us to stand firm in our faith, especially when it might cost us comfort or acceptance?
5. The Nicene Creed emerged as a unifying statement of Christian belief. How can creeds like this help the church maintain doctrinal clarity and unity today? How might they also serve as tools for personal faith and discipleship?

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).

B.K. Kuiper, The Church in History (Grand Rapids:L Wm. B. Eerdmans Publishing Company, 2001).

Unless otherwise indicated, 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.