Paul speaks of oral tradition as authoritative.
2 Thessalonians 2:15
Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.

2 Timothy 2:2
And the things that thou hast heard of me among many witnesses, the same commit thou to faithful men, who shall be able to teach others also.

1 Corinthians 11:2
Now I praise you, brethren, that ye remember me in all things, and keep the ordinances, as I delivered them to you.

1 Thessalonians 2:13
For this cause also thank we God without ceasing, because, when ye received the word of God which ye heard of us, ye received it not as the word of men, but as it is in truth, the word of God, which effectually worketh also in you that believe.

Early Christians followed apostolic tradition.
Acts 2:42
And they continued stedfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers.

The great commission by Christ was to preach not to write.
Matthew 28:19-20
Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Teaching them to observe all things whatsoever I have commanded you.

Bible hard to understand, gets distorted.
2 Peter 3:15-16
[Speaking of Paul's writings] 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.

More oral tradition.
2 John 1:12
Having many things to write unto you, I would not write with paper and ink: but I trust to come unto you, and speak face to face, that our joy may be full.

3 John 1:13-14
I had many things to write, but I will not with ink and pen write unto thee: but I trust I shall shortly see thee, and we shall speak face to face.

Against personal interpretation.
2 Peter 1:20-21
Knowing this first, that no prophecy of the scripture is of any private interpretation. 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.

Guidance needed to interpret scriptures.
Acts 8:30-31
And Philip ran thither to him, and heard him read the prophet Esaias, and said, "Understandest thou what thou readest?" And he said, "How can I, except some man should guide me?" And he desired Philip that he would come up and sit with him.