All Scripture—meaning what? You are dancing around the plain fact that the books of the canon were not inscribed on tablets of stone as was the law of Moses direct from the hand of God. Why these writings? Why ONLY these writings?
Because Jesus told no one else that the Holy Spirit would “bring to their remembrance”. Paul said to teach only what the apostles taught. And Jesus says in John 16: 13When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come.
You go right ahead and listen to the RCC, John Smith, or Muhammad but I’m staying with what the apostles taught because Jesus told them the Holy Spirit would “bring to their remembrance” and not any others.