To the question, "How do I know that my Redeemer lives?" some facilely respond "by faith." But what is this "by faith" whereby they know that there Redeemer lives? This is a question perhaps we have not explored deeply enough - - or at least not deeply enough in those areas which are by nature rather deep.
Lamentably, those responding to the question often make a fundamental kind of error, somehow believing that faith itself forms some perceptual-revelatory content whereby they are put in touch with the objectivity of the Word. The Word is imagined to be a content for thinking, willing, and doing, a content that faith somehow displays. Lutherans, of course, have always stressed the externality of the Word over and against its subjective appropriation. Because the Lutheran theological tradition has thematized externality, one would think it difficult were it to cast its eyes upon those having faith, were it to look upon the contour of faith rather than what faith is about. Clearly, for Lutherans, the reification of faith must be averted.
For this reason, believe, is perhaps helpful to think of faith adverbially. Like the adverbial theory of perception, an adverbial theory of faith would understand its subject as a way of being given, rather than as a content of givenness. In order to see this, let us review the distinction between the phenomenological experience of the subject's sense-data, and the way that the subject might know objects in the world.
Classically, sense-datum theorists claimed that there was something definite that was known perceptually, a phenomenological content that then could be judged as to how it related to the world. Accordingly, the world is conceived to have a definiteness to which the sense datum is related. Sometimes called an "act-object" theory of perception, the problem easily became how how to connect the givenness of the object of the act of givenness to the external world. It seems, in fact, that a type of perceptual dualism can easily arise, a dualism that holds between the sense-datum objects, and the putative mind-independent objects somehow causing them.
Adverbial theorists, however, take another avenue entirely. Instead of claiming that there are mind-dependent sense-datum objects interposed between the act of perception and the mind-independent external order, the adverbial theory declares that perception is of the external world, and that the thing putatively experienced, according to the sense-datum view, is merely a way in which the mind-independent world is experienced. It is not the experience of X that is present for an act of cognition or perception, but that the act of cognition or perception is a way of experiencing the world in a X-ly fashion.
An example might be helpful. According to a sense-datum theory, I can be given a red spot - - whether or not there is such a spot in the world. What appears to me is a red spot. The adverbial theory, alternatively, claims that I am experiencing the external world in a red-spottedly way, that is to say, I am being appeared to red-spottedly. While the theory successively opposes ontologizing perceptual content, it unfortunately does not adequately deal with the what exactly it is to be appeared to red-spottedly. While there is now no mystery how to get to the mind-independent world from an act of consciousness, there is great mystery in knowing precisely what the act of consciousness is by which one knows the world.
While neither the sense-datum and adverbial theories are cutting-edge these days in the philosophy of perception. their existence is useful for thinking through the nature of faith.
One might claim that faith provides a content in being "interposed" between the Word grasped and the subject grasping the Word. Accordingly, faith has a content that can be encountered, a content present to the subject that is in some way "caused" by the Word. Just as the mind-independent external object causes the putative sense-datum that is itself the object of the act of percepient's perceptual act, so too does the Word cause the content of faith, a content that is itself the object of the believer's act. Accordingly, there is an ontological priority to the Word over what the Word creates: the believer's faith. On this view, faith is made a substance, it is ontologized to become a thing existing between the believer and the Word.
But Lutherans would do best not to go down this track. Instead, it is far better to think of faith as a "way-of-being" the believer, as the way that Word is grasped by the believer. The Word is not available to us as a perceptual/conceptual content of the act of the believer's consciousness, but rather we are appeared to Word-ly. Faith is not an apprehension of the Word, but rather the Word's apprehension in us. Through faith we are appeared to Word-ly. Our experience of the Word is not a state in us that we can know, but rather is that by which the Word is itself known. Faith is not a theological reality, but the way in which theological reality is grasped. Accordingly, we are justified by grace not because of faith, but because our justification by grace happens faithfully. We are justified propter Christum, not propter fidem - - less anyone should grow confused.