You mention the early church.
The early church did NOT believe in OSAS.
It taught that persons could fall away by both apostacy and a sinful life.
Martin Luther did not believe in OSAS.
He believed that we are saved by grace alone and this is why he wanted to reform the CC.
He believed in repentence and a changed life.
It's easy to find this information on the net.
From Gemini:
No, Martin Luther did not believe in the modern doctrine of "Once Saved, Always Saved" (OSAS) or eternal security. While he emphasized salvation by grace through faith alone, Luther taught that a believer could fall from faith and lose their salvation.
The Puritan Board +2
- Possibility of Falling Away: Lutherans believe the Bible warns against falling from faith, meaning salvation is not guaranteed regardless of future actions or belief (1 Cor. 10:12, 1 Tim. 1:19).
- Repentance: Luther emphasized daily repentance rather than a one-time, irrevocable event.
- Assurance vs. Security: While rejecting OSAS, Luther and Lutheranism still teach that a believer can have full, confident assurance of their salvation in Christ at any given moment.
Reddit +4
Luther taught that God's grace is sufficient, but that faith must be maintained, and it is possible to abandon that trust.
OSAS was never taught in the church until Calvinism.
Calvinism teaches the perseverance of the saints.
About 200 years ago some theologians began to teach the idea of OSAS to mainline churches and this idea did catch on although most denominations do not adhere to this teaching to this day.
OSAS is a heretical (meaning non-orthodox) idea which is very recent.
Recent ideas are never in line with orthodox christianity.
This is also from Gemini....
- John Nelson Darby and the Plymouth Brethren (19th Century): Darby (1800–1882) played a crucial role in developing dispensationalism, which popularized a form of eternal security that became widespread in American evangelicalism and, later, Baptist theology.
- James Robinson Graves (19th Century): An influential figure in Southern Baptist history, Graves helped move this branch of Christianity toward a strong belief in the "security of the believer".
Key Distinction:
It is important to note that what Calvin taught was "Perseverance of the Saints"—the idea that God causes the true believer to endure to the end. The modern, popular form of "Once Saved, Always Saved" (sometimes called "Free Grace" theology) often diverges from Calvin by asserting that a person can have assurance of salvation even if they totally fall away from the faith, which differs from Calvin’s original emphasis on a persevering life.