Deen Lens

Understanding Christianity

A high-level, Muslim-authored overview of Christianity — its scale, history, scripture, and core doctrine — setting the stage for the rest of this section.

What is Christianity?

Christianity is the religion built around the life, teachings, death, and — for nearly all of its adherents — the resurrection of Jesus of Nazareth (peace be upon him), a Jewish preacher and healer active in Roman-occupied Judea in the early 1st century CE.1 It is, by most counts, the world’s largest religion: an estimated 2.3 billion people, roughly 29% of the world’s population, identified as Christian as of 2020.2

Christianity is not a single, unified institution. It comprises three broad historical families — the Roman Catholic Church, the Eastern and Oriental Orthodox churches, and the many Protestant traditions that emerged from the 16th-century Reformation — and, depending on how one counts, tens of thousands of individual denominations within them (one widely cited catalogue puts the figure near 45,000).3 These groups disagree with one another on questions as fundamental as the nature of God, and as specific as which day to observe as the Sabbath. The Christian Denominations page in this section compares twenty of the more prominent ones side by side, with estimated sizes and sources for each.

What holds this diversity together, loosely, is a shared scripture (the Bible), a shared central figure (Jesus), and — for the overwhelming majority, though not literally all self-identified Christians — a shared conviction that Jesus is God incarnate, the second person of a Trinity, who died to atone for the sins of humanity and rose from the dead. That last conviction is precisely where Islam parts ways with mainstream Christianity: the Qur’an honors Jesus as the Messiah, born of the Virgin Mary, but rejects his divinity. Is Jesus God? — is the question this section returns to from several directions, and it is worth understanding the Christian answer to it on its own terms before asking why Muslims answer differently.

The rest of this page summarizes that Christian answer, and the beliefs built on it, at a high level; dedicated pages elsewhere in this section go into far more depth on each individual topic.

Holy books

Christians hold as scripture the Bible, a collection of writings divided into the Old Testament (broadly, though not identically, corresponding to the Hebrew Bible of Judaism) and the New Testament (an account of Jesus’s life and the early church, along with letters attributed to Paul and others). Christians generally read the Old Testament through the lens of the New Testament’s claims about its fulfillment. The exact contents of the Old Testament vary by tradition — Catholic and Orthodox Bibles include several books (the Apocrypha, or Deuterocanon) that most Protestant Bibles exclude. See The Bible for how these collections took shape, and Is the Injeel (Gospel) Corrupted? for how the New Testament’s authorship and transmission are understood historically.

Nature of God

Christianity can be broadly categorized into two groups by how they answer the question above: Unitarian and Trinitarian. The former holds that God is One and that Jesus is not God but the Messiah — a minority position historically, though not a new one. The latter, which is the position of the large majority of Christians and of every major denomination compared on the Christian Denominations page, holds Jesus to be both the Messiah and God, following the doctrine of the Trinity: the Father, the Son — Jesus — and the Holy Spirit are each fully God, co-equal, distinct, and yet one. See The Trinity for how each side reads the biblical evidence, and its companion Questions & Answers page for a closer, verse-by-verse treatment.

Original sin

Trinitarian Christianity places heavy emphasis on the universality and severity of sin. The doctrine of Original Sin holds that all humans inherit sinfulness from Adam and Eve (peace be upon them), who committed the first sin — a condition held to be present from birth, not simply acquired through one’s own choices, and removable only through atonement. See Original Sin.

Law

Christian doctrine generally holds that the Ten Commandments (Exodus 20:1-17), given by God to Moses, are impossible for any person to keep perfectly. Any shortcoming is itself a sin, and — combined with the doctrine of Original Sin above — this is taken to make every human being a sinner in need of atonement, rather than an occasional lawbreaker who might simply repent and do better.

Atonement of sin

According to Trinitarian doctrine, sin cannot be forgiven by repentance alone; it requires a sacrificial atonement, a principle Christians trace to Old Testament sacrificial law (see Leviticus 17:11). To atone for the sins of all humankind at once, this reasoning holds, requires the sacrifice not of an animal but of a sinless human being — and only Jesus, being both sinless and divine, qualified. The crucifixion, in this account, was that atoning sacrifice, offered once for all people. See Atonement of Sins and its companion Questions & Answers page, along with Sin in Christian Thought for a closer look at the underlying concept of sin itself.

The crucifixion

The crucifixion of Jesus is understood, in this account, as an act of voluntary obedience to his Father: God the Son sacrificing himself to satisfy the demands of divine justice on behalf of humanity, thereby making those who have faith in him righteous before God. This is one of the sharpest points of disagreement with Islam, which holds that Jesus was not crucified in the way the Gospels describe, and rejects the idea that God’s forgiveness requires a blood sacrifice at all. See The Crucifixion.

Denominations

Christianity’s institutional history runs, in broad strokes, from a single early church, through the 1054 split between the Roman Catholic Church and the Eastern Orthodox Church (with the Oriental Orthodox churches having already separated centuries earlier, after the 451 Council of Chalcedon), to the 16th-century Protestant Reformation and its many subsequent divisions. One recurring theological fault line among Protestants is the claim that righteousness comes from faith rather than good works (see, for example, Philippians 3:9) — an emphasis not shared to the same degree by Roman Catholic and Orthodox Christians. See Christian Denominations for a fuller comparison, and Major Events in Christian History for the fuller timeline behind this summary.

Practice

Differences between Christian traditions show up not only in doctrine but in day-to-day practice: worship style (liturgical or informal), dietary customs (is pork permitted, and are there fasting seasons?), clerical and lay dress, whether and how Christmas and Easter are observed, and which day is kept as the Sabbath (historically Saturday, though most Christians today observe Sunday in commemoration of the resurrection). None of these differences are incidental — each usually traces back to a specific reading of scripture or church tradition.

Paul and the shape of the New Testament

Paul the Apostle — a former persecutor of the earliest Christians who described himself as converted by a vision of the risen Jesus — is by far the most influential figure in Christian history after Jesus himself, and his letters make up a large portion of the New Testament.4 Paul’s theology, especially his teaching that Gentile converts need not follow Jewish law, shaped the church that survived and spread; other early Jewish-Christian and Gnostic movements were eventually judged heretical and did not endure in comparable numbers. Most Christians alive today could fairly be described as Pauline Christians in this sense. See Is the Injeel (Gospel) Corrupted? for more on how the New Testament’s authorship is understood historically, and Opinions about Christianity for a closer look at that question.

This section exists to investigate the belief of our Christian brothers and sisters in good faith, and to lay out where and why Islam differs from it — through dialogue, respect, and sincerity, not point-scoring. The Answering Christianity section takes a more focused, question-and-answer approach to specific objections.

References

  1. "Christianity" — Encyclopedia Britannica and "History of early Christianity" — Encyclopedia Britannica, for Jesus's historical context and the movement's earliest development.
  2. "The World's Religious Groups: How Their Sizes Changed from 2010 to 2020" — Pew Research Center, for the global population and percentage figures.
  3. "World Christian Encyclopedia" — overview of the ~45,000-denomination figure and its counting methodology, based on the Center for the Study of Global Christianity's World Christian Database.
  4. "Christianity" — Encyclopedia Britannica, on Paul the Apostle's role in the early church.