Early Christians unquestionably regarded Scripture as authoritative.
The more difficult question is whether they held the later Reformation principle usually called sola Scriptura --- Scripture as the Church's uniquely infallible final norm.
The historical evidence should be examined rather than assumed.
Irenaeus is a useful test
In the late second century, Irenaeus fought Gnostic movements claiming authentic or secret Christian teaching.
He used Scripture extensively.
But he also appealed to:
- Apostolic Tradition;
- churches founded by Apostles;
- succession of bishops;
- the public faith preserved in those churches.
In Against Heresies III.4 he even considers what Christians would do if the Apostles had left no writings and points toward the tradition handed to those entrusted with the churches.
Read the source:
https://ccel.org/ccel/irenaeus/against_heresies_iii/anf01.ix.iv.v.html
Does that automatically disprove sola Scriptura?
Not automatically.
Protestant scholars can argue that the Apostolic tradition Irenaeus invokes substantially corresponds to the rule of faith found in Scripture and does not validate every later Catholic tradition.
That argument deserves consideration.
But Irenaeus does make one thing difficult to ignore:
early Christian authority operated through more than isolated private interpretation of biblical texts.
Ask the historical question
When Christians disagreed about the meaning of Christianity, what authorities did the early Church actually appeal to?
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