The rapid spread of Christianity in the first few centuries after Jesus Christ is one of the most miraculous stories in world history. The incredible expansion of Christianity is rooted in its message that although all people sin (Rom. 3:23), God has intervened in history through Jesus, who died to save people of all nations, races, classes, and backgrounds (John 3:16; Gal. 3:28).
By any measure, the church’s obedience to the Great Commission was a colossal success (Matt. 28:19-20; cf. Acts 1:8). Historian Kenneth Scott Latourette writes, “One of the most amazing and significant facts of history is that within five centuries of its birth Christianity won the professed allegiance of the overwhelming majority of the population of the Roman Empire and even support of the Roman state.” 
Latourette adds that Christianity’s spread is somewhat mysterious because the information from the period is “fragmentary” and “imperfect.”  Yet, even though the biographies of certain people and the history of some events are incomplete, it’s undeniable that Christianity spread like wildfire. It outlasted other movements and sects and ousted Rome’s largest and most influential religions.
Also see Who Was the First Christian Martyr? to learn more.
1. Christianity appeals to all nations, cultures, and societies
The teachings of Jesus appeal to all people, no matter their culture, ethnicity, or religious background. The gospel, which means “good news,” proclaims that although all people are born in sin, God sent his only son Jesus to save the world. Though the world isn’t the way God intended it to be because of sin, there is hope in this life and the next because Jesus came to seek and save the lost.
- Romans 3:23, “For all have sinned and fall short of the glory of God”
- John 3:16, “For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.”
- Luke 19:10, “For the Son of Man came to seek and to save the lost.”
- Matthew 28:19, “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit.”
A single nation doesn’t monopolize Christianity. Neither does a single ethnicity. Moreover, a person can become a Christian no matter their religious background. Those not born into the Christian faith aren’t considered second-class believers but valued, even esteemed, in the Church. The way of salvation in Christianity is exclusive (John 14:6; Acts 4:12), but the invitation to follow Jesus is inclusive.
- John 14:6, “Jesus said to him, ‘I am the way, and the truth, and the life. No one comes to the Father except through me.'”
- Acts 4:12, “And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved.”
Also see What Was the Great Schism in Christianity? to learn more.
2. Christianity appeals to people of every social standing
The founders of some religious belief systems prioritize converting wealthy people because their financial donations support salaries, infrastructure, and other projects. Though the New Testament gospel is equally for the rich and the poor, Jesus emphasized caring for social outcasts, like prisoners, beggars, many of whom had physical disabilities, and prostitutes.
- John 8:7, “Let him who is without sin among you be the first to throw a stone at her.” (Jesus protects an adulterous woman)
- Matthew 28:45, “Then he will answer them, saying, ‘Truly, I say to you, as you did not do it to one of the least of these, you did not do it to me.'” (Jesus identifies with social outcasts)
- Acts 2:45, “And they were selling their possessions and belongings and distributing the proceeds to all, as any had need.” (The first Christians took care of each others needs)
- Galatians 2:10, “Only, they asked us to remember the poor, the very thing I was eager to do.” (The Apostle Paul carried on Jesus’ legacy of carrying for the poor)
Christian history shows that sometimes dignitaries converted to Christianity, from Roman Emperors to kings to presidents. Yet, most of the time, the social outcasts in their society did first.
Christianity’s unique appeal to women
Historians know that Christianity uniquely appealed to women, unlike other faiths in the ancient world.
Rooted in the interactions that Jesus had with women of ill repute, like the women caught in adultery, the Samaritan woman, the woman bleeding for 12 years, and Mary Magdelene, Christian missionaries shared the gospel with women, promoted their safety in society, and their value in the family.
In the modern era, the same conviction has led Christian missionaries to educate women, fight for their civil rights, and seek justice in cultures where rape, prostitution, and child brides are common.
Also see How To Become A Christian to learn more.
3. Persecution accelerated the spread of Christianity
Countless people have attempted to suppress and even eliminate Christianity through persecution. History shows that if an individual or government wants to stop the spread of Christianity, the very last thing they should do is persecute believers. Perseverance amid persecution is one of the most powerful illustrations of the authenticity of a Christian’s devotion.
The early church theologian Tertullian once said, “The blood of martyrs is the seed of the church.” This insight means that when a person dies for their faith, it’s often a catalyst for greater devotion to God for those that witness it. The story of Stephen, the first Christian martyr, and his influence on the Apostle Paul is evidence of Tertullian’s statement.
Luke records that as the religious authorities stoned him, Stephen said, “Lord Jesus, receive my spirit.” He then fell to his knees and cried, “Lord, do not hold this sin against them” before he died. (Acts 7:59-60). The anger, hate, and cruelty that permeated the hearts of the killers didn’t characterize Stephen, who was peaceful, prayerful, and forgiving.
One of the persecutors who witnessed Stephen’s death was Saul, later named Paul. Shortly after Stephen’s death, the risen Jesus intercepted Paul on his way to Damascus to persecute Christians (Acts 9:1-8). Jesus called Paul, commissioned him, and equipped him to be a missionary.
As a result, Paul became one of the most important converts in the history of the Christian church. For example, he wrote 13 of the 27 books of the New Testament. Paul’s influence on the Bible, the church, doctrine, and the spread of Christianity can’t be overstated.
Also see What Are Christian Apologetics? to learn more.
4. Christian missionaries utilized development and technology
Roman roads were one way Christians used modern development to their advantage. In the centuries before Jesus, the Romans built a vast system of roads for ease of transportation and trade, which brought social and economic unity to the empire.
In obedience to the Great Commission (Matt. 28:19-20), the first missionaries, like the Apostle Paul, used Roman roads to quickly and efficiently travel from one town to another to preach the gospel.
Another example of Christians embracing new developments and technology to spread the gospel is their use of the codex. “Codex” is the name for a piece of literature in book form.
Before the codex, people mostly wrote on scrolls. The codex contained more space than scrolls and was much easier to transport. This development was significant to Christians because of their high value of the Bible (e.g. John 17:17; 2 Tim. 3:16-17).
5. God called, equipped, guided and empowered missionaries
Historians know that the above facts significantly contribute to Christianity’s spread in the Roman Empire. Biographers, theologians, and experts on Rome continue to work to piece together the story in its entirety. However, even when every detail is known someday, Christianity’s expansion will be difficult to explain apart from God’s plan, guidance, and favor.
Church historian Bruce Shelley writes, “By ordinary standards nothing could have been less likely to succeed. But believers have always insisted that God was at work in this movement.” 
The first converts and missionaries had God’s power to spread the gospel. Jesus told his followers, “But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth” (Acts 1:8).
Additionally, the first Christians had Jesus’ presence with them. After he told them to “make disciples of all nations,” Jesus promised, “I am with you always, to the end of the age” (Matt. 28:19-20).
Also see Where Do Christians Worship? to learn more.
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