More Sure than Oral Apostolic Tradition
The aposltes realized that Apostolic "oral" teaching had its limitations after their death and so Peter not only wanted something "more sure" to leave them after his departure:
2 Pet. 1:13 Yea, I think it meet, as long as I am in this tabernacle, to stir you up by putting you in remembrance;
14 Knowing that shortly I must put off this my tabernacle, even as our Lord Jesus Christ hath shewed me.
15 Moreover I will endeavour that ye may be able after my decease to have these things always in remembrance.
He reminded them of his "oral" witness to a specific event but no doubt the gospel account of this event was already written and Peter instructs them to take heed to something "more sure" than oral witness by the Apostles:
2 Pet. 1:16 ¶ For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.
17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.
18 And this voice which came from heaven we heard, when we were with him in the holy mount.
19 ¶ We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts:
20 Knowing this first, that no prophecy of the scripture is of any private interpretation.
21 For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost.
Peter is telling his readers that his written revelation of this event (and other Apostolic writings of it) are "more sure" than his oral presentation of this same event. He is claiming inspiration for his writings as much as he goes right on to claim inspiration for "ALL" the epistles written by Paul:
2 Pet. 3:16 As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.
The process in producing the Old Testament Scriptures is the same as with the New Testament Scriptures. It is first given in oral teaching and then put into writing as inspired scriptures. The written supersedes the oral as it is "more sure" in preserving the truth as it is placed in a contextual self-defining patten so that scripture interprets scripture.