But, in life and death, we seek truth and find it in texts all the time: I learn that someone loves me in a letter. I learn that my father has died in a telegram. In an ancient letter from Paul, I might learn that God has suffered for me and died for me because of His Love for me. I might be invited to give up my pride and belief in my own wisdom and seek after God in prayer and humility. I might find the God who died for me when I do so.

As to your objectins: People do disagree about texts. You may read the same love letter and conclude that she does not love me; the same telegram and conclude that my father has not died. You may not trust the sender or may be confused by the words. Texts may convincingly convey truths to one person and not to another, but that does not mean that they cannot convey truth at all. Lawyers may disagree about the meaning of the United States Code, but that does not mean USC is not an authority.

If you are interested in philosophical treatments of these issues, you might try Nicholas Wolterstorff, Divine Discourse: Philosophical reflections on the claim that God speaks (Cambridge: Cambridge University Press, 1995) or Richard Swinburne’s book Revelation, 1991, http://www.oup.com/uk/catalogue/?ci=9780198239680