What history teaches about "The Great Apostasy"

I have just spent the past few hours doing some research on this topic. I've also been engrossed in ex-Mormon YouTube, partly because I've always been interested in the origins of the theology and because I wanted to get to the heart of why there were so many "revivalist" or "restorationist" movements in the 19th century with New York state origins. That alone is an interesting thread. But then I ventured into studying the early "church fathers", like Clement of Rome, Ignatius, Eusebius and Iraneaus and came across something interesting. In the 2nd century, Gnosticism was taking root. I had heard about "Gnostics" and "Gnosticism" but never really looked into it. What I learned, with the help of ChatGPT:

“Gnosticism” isn’t one group.

It’s a family of early Christian-adjacent religious movements (1st–3rd century) that taught:

1. The physical world is a tragic mistake.

Not created by the true God.

Created instead by a flawed, ignorant lesser being—the Demiurge.

This is the key point that separated them from Jewish and Christian belief, where creation is good.

2. Humans contain a trapped divine spark.

Something from the true God is imprisoned in our physical, flawed bodies.

3. Salvation comes by gnōsis—secret knowledge.

• Not faith.
• Not repentance.
• Not ethical transformation.
• Salvation = learning the cosmic backstory of the universe and remembering your true origin.

4. Jesus is a revealer, not a redeemer.

In most Gnostic systems:

• Jesus did not have a physical body

• Jesus did not suffer

• Jesus did not die

• Jesus came as a disguised messenger from the higher God

• His mission was to awaken the elect with secret knowledge

This is anti-incarnational and anti-resurrectional—a total inversion of apostolic Christianity.

5. Scriptures are read through secret codes.

Gnostics re-read Genesis as:

• the serpent = liberator

• the creator = jailer

• Adam and Eve = early “Gnostics”

• the fall = the moment humans learned the truth

• salvation = escape from the material world

This was a light bulb moment. First, the Gnostics and Gnosticism sound precisely like the type of groups that the apostles warned about. The ones that would sow division in the early church. For instance, Paul warned about those with "special knowledge". Gnosticism derives its name from gnosis, knowledge. (1 Cor. 8:1); Warnings about those preaching a different gospel, or claiming special revelations (1 Cor. 11:8, Galation 1:8) The letter to Colossians is understood to be a direct challenge to proto-Gnosticism.

Second, in many respects, Gnosticism sounds more akin to 19th century movements: Mormons have very imaginative theology, with different levels of heaven, secret knowledge, rituals, new scriptures (Book of Mormon, Pearl of Great Price, Doctrine and Covenants); Adventist movement had "secret knowledge" in numerology, predictions/prophecies. These ideas were picked up by their "children", SDA, JW's, Campbellites, etc.

These latter groups teach that the "Great Apostasy" was the corruption of the "true church" and that they are restoring it. They all teach that the apostasy manifested itself as the Catholic church. However, when the history is studied, it turns out that by the third century, these early church fathers were already combatting the apostasy, in the form of the Gnostic movement. They did so with a three pronged strategy: canon, creed, apostolic succession, i.e, tracing all teaching back to the bishops of each major city who could in turn trace their teachings to the apostles who taught "publicly and from house to house" (not in the mormon/JW way, knocking on doors, but teaching in the the small "house churches" of the first century.

The three prongs:

1. The Canon — “These are the books the apostles left us.”

Problem: Gnostic groups produced many new “gospels” and claimed secret revelations.

Response: The church identified the writings that came from apostolic communities—Matthew, Mark, Luke, John, Paul’s letters, Acts, and the rest of what became the New Testament

Purpose: To stop endless new revelations and anchor the faith to a shared, public set of texts.

Effect: Gnostic scriptures lost authority; the church gained a common, stable story.

1. The Creed — “This is what the apostles taught.

Problem: Gnostics denied the incarnation, Jesus’ real body, His death, and the physical resurrection.

Response: The church created short, memorized statements of belief (proto-creeds that became the Apostles’ Creed) emphasizing the very points Gnostics rejected: one Creator God, Jesus born in the flesh, suffered, died, was buried, rose bodily, and the resurrection of the body.

Purpose: To set doctrinal guardrails around the apostolic faith.

Effect: Teachers promoting “secret gospels” or anti-incarnational theology were exposed immediately.

1. Apostolic Succession — “These are the teachers trained by the apostles.”

Problem: Gnostic teachers claimed the apostles gave them secret doctrines privately.

Response: The church traced the line of bishops back to the apostles, emphasizing public teaching, public communities, and public succession. Irenaeus famously said: “We can name the bishops of every city back to the apostles. Gnostics cannot.”

Purpose: To prove continuity and expose private, unverified claims of authority.

Effect: Orthodoxy became defined as the public, traceable lineage of teaching, not hidden revelations.

TL;DR:

Canon set the boundaries of Scripture,

Creeds set the boundaries of belief,

Apostolic succession set the boundaries of legitimate teaching.

Together they formed a coordinated defense that crushed Gnostic movements and preserved the apostolic faith.

I’m not making an argument for Catholic or Orthodox theology here. I’m explaining how the earliest Christian communities responded to real intellectual and spiritual threats that were already fracturing the movement in the first and second centuries. When you look at the evidence as a historian—not as an apologist—you see that the canon, the creeds, and the idea of apostolic succession didn’t appear as power grabs or later inventions. They were practical solutions the early church built to preserve a recognizable form of apostolic Christianity in the face of rival groups claiming secret revelations and alternative Jesuses. Whether one agrees with the later institutional churches or not, this is simply how the history unfolded. The idea—popular in several 19th-century restorationist movements—that Christianity became hopelessly corrupt shortly after the apostles died simply doesn’t match what actually happened on the ground. The earliest documented challenges to apostolic teaching weren’t medieval institutions or later Catholic structures; they were 1st- and 2nd-century movements like the Gnostics, who rewrote the Christian story entirely. The historical record shows the early church trying to hold the center, not losing it: the canon, the creeds, and apostolic succession were built as defenses against these early distortions, not as departures from the faith. So when we look at this period as historians, the “Great Apostasy” framework just doesn’t align with the evidence.