Although I think I understand your point, and at least partly agree with it, it can be misleading. When most of us refer to the need to use written words as an authority, we are talking about the inspiration of Scripture, meaning that God gave us written words to help us retain the truth.
Obviously, it's equally important to hear the word of God in our heart, or in our conscience. Without this spiritual sense of God's word, written words can become very weak and almost nonsensical. To apply a word from God properly, in the right context, we need guidance from God Himself. His living word must accompany written words to obtain revelation from them. And we need spiritual virtue from God to put these words into action.
We just need to recognize that God set up testimonies to be written so that the truth could be preserved. As such, the Scriptures are to be used to retain orthodoxy, to correct heresy, to edify and to enlighten, so that we all grow up into one man, Christ.