"Conclusion, That the authority of Scripture is founded on its being spoken by God..." This is your proof? Soudds like "it is because I say it is" type of "proof." If all else fails we will just use a dogmatic sledge hammer. Please, let's move on. It's obvious you don't know and can't answer it.
You obviously misread Calvin. Scripture is no more open to proof than God is. God isn’t mathematics. God isn’t someone we dissect. God, if he exists at all, is too big for our minds.
Therefore, you believe or you do not. But reason cannot be an infallible guide, because your reason is inadequate for the task.
Please understand! I’m not even TRYING to prove Scripture is God’s Word to you. I assume it, and go from there. It is part of my belief that NOTHING I do or say will ‘prove’ God or Scripture.
Now, once one assumes Scripture is God’s Word, and infallible, then those who agree can use it for rational discussion about their beliefs.
But I have never tried to prove God or Scripture to you. That is above my pay grade. You cannot know God by reason. It takes revelation, and I’m not divine, so I can’t give it.