No one is disputing that the Bible is the word of God, or that it is trustworthy, but is it (or ought it be) the ONLY source of teaching and practice for God's Church?
It seems to me that if the inspired word of God was meant to be the sole authority it was say so, somewhere in the scriptures.
Christ chose and appointed men over His Church. He gave them instructions to go out and preach the Gospel. The scriptures tell us He spoke parables to the multitudes, but to His disciples He explained all things. The scriptures tell us that Christ did many others things, that were not written down.
Christ built a Church during His ministry. He did not write, or have scribed, anything. When He commissioned the disciples to go out He did not give instructions to pass out the written word.
Scriptures tell us to hold to the traditions learned, by word or epistle.
2Th 2:15 (2:14) Therefore, brethren, stand fast: and hold the traditions, which you have learned, whether by word or by our epistle.
Scriptures tell us the Church is the pillar and ground of truth, and the place that the manifold wisdom of God may be made known.
1Ti 3:15 But if I tarry long, that thou mayest know how thou oughtest to behave thyself in the house of God, which is the church of the living God, the pillar and ground of the truth.
Eph 3:10 That the manifold wisdom of God may be made known to the principalities and powers in heavenly places through the church,
Scriptures tell us that they are 'profitable' to teach, reprove, correct, and to instruct. Profitable goes with those things and is not solely sufficient. Teaching was a commandment of Christ to the disciples.
2Ti 3:16 All scripture, inspired of God, is profitable to teach, to reprove, to correct, to instruct in justice:
Mat 28:19 Going therefore, teach ye all nations: baptizing them in the name of the Father and of the Son and of the Holy Ghost.
If scriptures were the sole authority why would scriptures tell us to obey our prelates/leaders?
Heb 13:17 Obey your prelates and be subject to them. For they watch as being to render an account of your souls: that they may do this with joy and not with grief. For this is not expedient for you.
Scriptures tell us God set the order of authority in His Church.
1Co 12:28 And God indeed hath set some in the church; first apostles, secondly prophets, thirdly doctors: after that miracles: then the graces of healings, helps, governments, kinds of tongues, interpretations of speeches.
Maybe I am misunderstanding the concept of 'sole authority', but for me sole authority is all that is needed and scriptures do not say that. Scriptures become subject to the interpretation of man. One has to exert an authority to say his interpretation is correct over another person's interpretation. If scriptures were the sole authority, wouldn't we all have the same interpretation?