Upon the writing of Scriptures.
Hebrews 1 states:
1 God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, 2 in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world.
This passage showed that God used the prophets in various ways to communicate. This is why one may take the OT as authoritative.
Paul states in Galatians:
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
9 As we said before, so say I now again, if any man preach any other gospel unto you than that ye have received, let him be accursed.
This passage shows the basic view of what Paul not only focused upon as the message, but also the
authority level - that there was a judgment for not following the teaching of the gospel of the death, burial, and resurrection of the Lord Jesus Christ as eye witnessed by the Apostles. The opening of Galatians shares that Paul is included as an Apostle, therefore his teaching must be aligned also with the Gospel, or he too is accursed.
Paul did not assume all that he spoke or wrote was "Scripture."
Paul states in 1 Corinthians:
12 But to the rest I say, not the Lord, that if any brother has a wife...
This passage indicates that Paul did receive special communication from the Lord concerning matters he taught, and also there were times when he had to state his opinion and not as a message from the Lord. Does that mean that opinion carried the same weight as Scriptures? Could it be that such an opinion would not be "accursed" if it was wrong? Certainly not! Rather, because Paul wrote both "from the Lord" and "I say" statements, there is a level of authority that Paul recognized, lost in the modern church that will even use the opinion as if it were "from the Lord."
Paul states in 1 Corinthians 4:
15 For if you were to have countless tutors in Christ, yet you would not have many fathers, for in Christ Jesus I became your father through the gospel. 16 Therefore I exhort you, be imitators of me.
This indicates that because Paul considered himself a father figure and not a tutor/teacher, only, the assembly should follow
his example as he in turn has followed Christ Jesus.
Paul states in 1 Corinthians 2:
“Things which eye has not seen and ear has not heard,
And which have not entered the heart of man,
All that God has prepared for those who love Him.”
10 For to us God revealed
them through the Spirit; for the Spirit searches all things, even the depths of God. 11 For who among men knows the
thoughts of a man except the spirit of the man which is in him? Even so the
thoughts of God no one knows except the Spirit of God. 12 Now we have received, not the spirit of the world, but the Spirit who is from God, so that we may know the things freely given to us by God, 13 which things we also speak, not in words taught by human wisdom, but in those taught by the Spirit, combining spiritual
thoughts with spiritual
words.
Paul relies upon the teaching work of God through the Holy Spirit, not human wisdom. That teaching was also spoken as Godly wisdom that combined spiritual with spiritual. The "thoughts" and "words" are inputted into the statement because (imo) Paul is showing how his thoughts and thinking were from the Holy Spirit and therefore his worlds, also - spiritual to spiritual, (as a man thinks so is he).
Therefore, there is solid reason for the church to take what Paul and others wrote as Scriptures.
What I maintain is that the writers did not place that level of authority upon what they wrote, but considered they were writing what was given to them by the Holy Spirit (teaching all things of Christ) as explanation and teaching to the assemblies. As they received and recalled the teaching of Christ, the Apostles also taught to the assemblies. As such, they possibly considered themselves more as an electrical cord than a generator or originator of the power.
There is no doubt that Paul considered his writing should and would be taken as authoritative, and perhaps even to be placed (as one trained in Rabbinical school) at the level of esteem along with the rabbinical scholarly writing of note in his day.
What cannot be assumed is that Paul or any other writer of the NT knew that they were actually forming a New Testament or that such a Testament would one day emerge in the church. There is no Scripture foundation for such thinking that I have found. Should one find something I missed, then as with all matters, I remain open to a review and change IF shown by Scriptures the need.
It is also not a bad principle to hold that the Cannon of Scriptures was formed by God as the assemblies held onto and esteemed certain writings as more authoritative and more "of the Spirit of God" than other writings. Eventually that systematic weeding out, led to groups that placed a certain "stamp of approval" upon what is now the NT.