"We believe, teach, and confess that the only rule and norm according to which all teachings, together with all teachers, should be evaluated and judged [2 Timothy 3:15-17] are the prophetic and apostolic Scriptures of the Old and New Testament alone. For it is written in Psalm 119:105, "Your word is a light to my feet and a guide to my path." St. Paul has written, "even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed" (Galatians 1:8)."
Formula of Concord: Epitome 7
"In this way the distinction between the Holy Scriptures of the Old and New Testament and all other writings is preserved. The Holy Scriptures alone remain the judge, rule, and norm. According to them - as the only touchstone - all teachings shall and must be discerned and judged to see whether they are good or evil [1 Thessalonians 5:21-22], right or wrong."
Lutheran Confessional Documents
Formula of Concord: Epitome 2
"However, other writings by ancient or modern teachers - no matter whose name they bear - must not be regarded as equal to the Holy Scriptures. All of them are subject to the Scriptures [1 Corinthians 14:32]. Other writings should not be received in any way or as anything more than witness to show how this pure doctrine of the prophets and apostles was preserved after the time of the apostles, and at what places."
Lutheran Confessional Documents: The Book of Concord (1580)
The Three Universal or Ecumenical Creeds: The Apostles' Creed, the Nicene Creed, The Athanasian Creed
The Augsburg Confession (1530)
The Apology of the Augsburg Confession (1531)
The Smalcald Articles (1537)
The Power and Primacy of the Pope (1537)
The Small Catechism (1529)
The Large Catechism (1529)
The Formula of Concord: Epitome (1577)
The Formula of Concord: Solid Declaration (1577)
Formula of Concord: Epitome 6, 8
As announced above, all teachings are to be conformed in this way. What is contrary to these confessions is to be rejected and condemned, as opposed to the unanimous declaration of our faith.
The other symbols and writings mentioned above are not judges like Holy Scripture. They are only a testimony and declaration of the faith. They show how the Holy Scriptures have been understood and explained in regard to controverted articles in God's Church by those living at that time. Also, they show how the opposite teaching was rejected and condemned.