The Lutheran Confessions are the true and accurate summary of the Holy Scriptures. Many churches say they believe in the Bible. But whose interpretation of the Bible?  Jesus taught the disciples. The Disciples became the Apostles after the Ascension of Christ into Heaven. The Apostles instructed the Church Fathers, who wrote thousands of pages of documents, books, and taught about what they had learned. Names like Augustine, Jerome, Clement  and others. 

That apostolic teaching was passed down to the Reformers: Luther, Melanchthon, and Chemnitz, among others. It was that teaching that brought the church back from the error of its ways in the middle ages. 

A confessional church holds to the teachings in the Book of Concord because (Quia) it is the true exposition of Scripture; Non-confessional churches hold to a Quantenus (Insofar as) subscription which means: "We believe in the confessions insofar as there is no conflict with scripture, in which case, we will hold with scripture". Sounds good, doesn't it?  What this really means is this: We believe some parts of the Bible, because it suits our world-view, or meets with public approval, etc. But other parts, which are inconvenient or un-popular, with the modern culture we will disregard. 

You see, quite simply, Faith Lutheran believes in the whole Bible, not just parts of it.