“Jesus answered them, ‘Is it not written in your Law, “I said, you are gods”? If he called them gods to whom the word of God came—and scripture cannot be broken— do you say of him whom the Father consecrated and sent into the world, “You are blaspheming,” because I said, “I am the Son of God”?’”
One way to read this is to see Jesus as simply stating facts about the scriptures. Indeed, the things he said are things the Pharisees believed.
Another way to read it, however, is as Jesus speaking to them within their own accepted ideas to point out a contradiction. In this reading, the phrase “scripture cannot be broken” was meant ironically as in “Your scriptures says this and since you believe your scriptures are inspired you must answer the question.” In other words, Jesus is using their own belief system against them. (This is not to say that Jesus didn’t believe we are gods, but that’s a topic for another time.) This reading is supported by the fact that Jesus said “your Law” and not “our Law,” thus refusing to identify with their way of thinking.
2 Peter 1:19-21
“And we have the prophetic word more fully confirmed, to which you will do well to pay attention as to a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts, knowing this first of all, that no prophecy of Scripture comes from someone’s own interpretation. For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit.”
Notice it only says “no prophecy was ever produced by the will of man,” and doesn’t say writings. Prophesying is one matter. Writing things down is another. Not all prophesy has been written down.
2 Peter 3:15-16
“…just as also our beloved brother Paul, according to the wisdom given him, wrote to you, as also in all his letters, speaking in them of these things, in which are some things hard to understand, which the untaught and unstable distort, as they do also the rest of the scriptures, to their own destruction.”
Peter states that Paul’s writings are scripture. Okay. But where is the statement that Peter’s writings are scripture? There is none. And since there is none, how do we know that Peter’s statement, not having been stated to be scripture, is inspired and therefore correct? Again, circular reasoning is at work here. To deduce that Peter’s claim was correct, we would have to assume that God inspired him to write it.
Moreover, even if Peter did equate Paul’s letters with the rest of scriptures, it was only in reference to the original recipients of the letters, not us. It’s an assumption to take it that Peter meant that they have the same kind of relevance and status for believers at every time from that point on.