Martin Luther had a lot to say about the Bible, and this quote is one example. The term “Word” implies communication, and in this case we’re talking about the Word of (or from) God. So how do we hear God’s Word to us? Here’s Luther’s answer:
They . . . desire to know who he [God] is and not to regard what he says, while he desires them first to listen; then they will know who he is. The rule is: Listen and allow the Word to make the beginning; then the knowing will nicely follow. If, however, you do not listen, then you will never know anything. For it is decreed: God will not be seen, known, or comprehended except through his Word alone. Whatever, therefore, one undertakes for salvation apart from the Word is in vain. God will not respond to that. He will not have it. He will not tolerate it any other way. Therefore, let his Book, in which he speaks with you, be commended to you; for he did not cause it to be written for no purpose. He did not want us to let it lie there in neglect, as if he were speaking with mice under the bench or with flies on the pulpit. We are to read it, to think and speak about it, and to study it, certain that he himself (not an angel or a creature) is speaking with us in it.