How can a young man keep his way pure?
By guarding it according to your word.
With my whole heart I seek you;
let me not wander from your commandments!
I have stored up your word in my heart,
that I might not sin against you.
Blessed are you, O Lord;
teach me your statutes!
With my lips I declare
all the rules of your mouth.
In the way of your testimonies I delight
as much as in all riches.
I will meditate on your precepts
and fix my eyes on your ways.
I will delight in your statutes;
I will not forget your word.

Psalm 119:9-16 (ESV)

Was the original purpose of the Lutheran confessions to serve as the lens through which the Scriptures must be understood? Are the Scriptures so ambiguous that they require authoritative human interpretation? No, the Lutheran confessions were derived directly from the light of the Scriptures, not from previous confessions or from quotations of church fathers. In fact, the Lutheran confessions do not offer yet another interpretation of Scripture, as Franz Pieper pointed out (Christian Dogmatics, Concordia Publishing House: St. Louis, Missouri, 1950, Vol. 1, p. 367):

The thought common in our day that all church bodies stand on Scripture and differ only in their interpretation of it is not in accordance with the facts. The Roman Catholic Church does not stand on Scripture, but on the papal interpretation of Scripture. The Reformed Churches, as far as they differ from the Lutheran Church, do not stand on Scripture, but on Zwingli’s, Calvin’s, etc. interpretation of Scripture. The Lutheran Church, however, does not stand on interpretation of Scripture, but on Scripture itself. This is not a mere assertion. It can be proved by induction in the face of universal contradiction.

The reason no human interpretation is needed is that Scripture interprets itself (ibid., pp. 363-364):

Luther is unalterably convinced that God gave Holy Scripture such a form that the entire Christian doctrine is revealed and submitted in passages which need no ‘exegesis’ (exegesis in the sense of removing obscurities). He who would determine the meaning of the clear passages through still other passages engages in a work of interminable adjustments, makes the entire Scriptures uncertain and obscure, and converts them into an inextricable chaos. Yes, there is the rule: ‘One passage must be explained by another,’ but, as Luther adds immediately: ‘Namely, a doubtful and obscure passage… must be explained by means of a clear and certain passage.

An author of the Formula of Concord similarly explained what it means for Scripture to interpret Scripture (Chemnitz, M., J. A. O. Preus, trans., The Lord’s Supper, Concordia Publishing House: St. Louis, Missouri, 1979, pp. 68-69):

For Scripture, especially when it treats of dogmas, because it is not of private interpretation, interprets itself either in the same passage or in other passages were the same dogma is touched on. Because of this, the same dogma is fully treated and repeated in various passages of Scripture in such a way that no one can dream up his own personal interpretation but must derive it from Scripture itself. For the same dogma is repeated on the basis of either the same or similar words which have the same meaning and set forth the same teaching, so that the simple, proper, and natural meaning of the passage may be confirmed… Or if something in one passage is too brief or obscure because of the puzzling nature of the figures of speech, Scripture will explain and interpret it in other passages where the same doctrine is repeated more fully, clearly, and openly, using proper, clear, natural, and commonly understood words.

With confessions derived from the word of God alone, it might be thought that Lutherans would not cite human authorities as proof texts instead of clear passages of Scripture. However, these words of August Pieper are as true today as they were in the beginning of the twentieth century (Mark Braun, “The Wauwatosa Gospel,” in Lord Jesus Christ, Will You Not Stay: Essays in Honor of Ronald Feuerhahn on the Occasion of his Sixty-Fifth Birthday, pp. 131-152, 2002, available from Concordia Publishing House, p. 24 of this Charis article):

This caused people to think that the point that was presented or discussed was sufficiently established by the quotations from Luther and the fathers without a study of Scripture itself.  It even led to this that later one did not stop with quoting Luther and the old fathers, but now one also quoted Walther and other celebrities for proof of the correct doctrine. The subject of study for new essays became not so much Scripture as the essays in the old synodical reports, and quotations from them were frequently used instead of proof from Scripture.

As August Pieper warned, implicit trust in any human authority for the correct interpretation of Scripture is idolatry leading to additional errors (ibid., p. 25):

We intend in the future to pursue scriptural study even more faithfully than before. . . . We submit in advance to the least word of Scripture that opposes us, no matter from whom it may come. But we submit to no man, be his name Luther or Walther, Chemnitz or Hoenecke, Gerhard or Stoeckhardt, so long as we have clear Scripture on our side. . . . We esteem the fathers highly, far higher than ourselves as far more learned and more devout than we are. Therefore, we want to use them, particularly Luther, as guides to Scripture, and to test their doctrines a hundred times before we reject them. But authorities equal to Scripture or opposed to Scripture they may never become for us, or we shall be practicing idolatry. . . . We renounce this authority-theology anew. It causes so much damage to the church. It is unfaithfulness to the Lord; slavery to men; it brings errors with it.

For extreme examples of inappropriate appeals to human authority, some say the Lutheran confessions require believing in the Perpetual Virginity and practicing communion weekly even though they cannot provide anything resembling Scriptural proof. They believe aspects of the confessions that are not expositions of any Scripture, on the direct authority of the confessions. That indicates severe misunderstanding of the historical context and purpose of the confessions as solemn affirmations of Scriptural teaching. A proper response is, “Where does the Bible say that?”

A less extreme but more common example is assuming the Lutheran fathers must have based their teaching about some topic on Scripture instead of carefully examining what the Scriptures actually say on the topic. Taking Luther’s or the synod’s word for it is never acceptable when it comes to doctrine, not even on a busy day.

The fathers should not be cited as final authorities, saying something like, “August Pieper said so, so you should believe it, too.” At the same time, they can be cited profitably, for instance, “See August Pieper for the exegetical details” or “I realized this thanks to Chemnitz’s insistence on the clear meaning of those Scriptures, which I had somehow overlooked.”

In discussions with other Lutherans, there is a time to appeal to the confessions as secondary authorities: when there is mutual agreement about their meaning. When there is not, it is usually counterproductive to spend much time arguing about what they really say, especially since we have no promise about their perspicuity. It is then time to say, “Look, the Teacher himself said so in clear language, so it’s not really up for interpretation.” He promises to enlighten us with his own words.