Two quotes on the sufficiency of Scripture:
Some persons think they can know God by means of their own human reason. But reason is a blind ally spiritually. It has always been the great minds exercising their powers apart from the Word of God who have produced the great heresies. Some think they can discover God by listening to a so-called ‘inner voice.’ But the voice is often nothing more than an expression of their own inner desires. Quite a few think that spiritual truths can be verified by supernatural events or miracles. But the Bible everywhere teaches that even miracles will not lead men and women to understand and receive God’s truth unless they themselves are illuminated by the Bible (see Luke 16:31). I believe that we can state categorically that there is no knowledge apart from Jesus Christ and that there is no knowledge of Jesus Christ apart from a knowledge of the Bible. – James Montgomery Boice
I have covenanted with my Lord that he should not send me visions or dreams or even angels. I am content with this gift of the Scriptures, which teaches and supplies all that is necessary, both for this life and that which is to come. – Martin Luther
Note: A series of 3 posts on the sufficiency of Scripture: How does God Speak to us Today?