Which is as circular as saying,
Well, how can you be so sure?
Because the Catholic Church says so.
Well then, how do you know that the Catholic Church is 100% correct?
Because the Catholic Church says it (conditionally) cannot err.
In contrast to this circularity, in both cases appeal is made to external evidential warrant, that Scripture is of God, or that the the Catholic Church is, and thereby one knows Scripture is.
The problem with the latter is that in Catholic theology it is taught that one cannot discover the contents of revelation and believe in the Bible and find in it the object of his faith until he has previously made an act of faith in her, as they have to be told what is of God by her.
However, if it is allowed that souls can discover the RCC as being of God before they submit to her, then how that it is not allowed that they can discover Scripture as being so before they submit to her?
And the fact is that long before there was a church of Rome who presumed this, then common people rightly ascertained both men and writings of God as being of God. Even in dissent from the historical magisterium, and which is how the NT church began, contrary to the Catholic model for ascertaining and assurance of Truth (but not contrary to the non-infallible authority of leadership).
I can’t disagree. How do you know what Krishna/Baghavad Gita said was wrong? How can you be so sure?
How can you be sure that Islam is wrong? Or the Marxists? Or the Scientologists? How can you know?
Actually, you are missing one thing that verifies the Biblical text: prophetic writings. How many OT prophesies came to fruition in terms of Jesus Christ? Was not the rise and fall of Greece predicted by the OT?
As for the NT, depending on the earliest date of the earliest Synoptic Gospel, the fall of Jerusalem is predicted by Jesus, and was recorded before it happened.
Does any other source have that track record?