What is an 'unconditional subscription' to the Confessions (Book of Concord)?

Confessional Lutheran pastors are required to “subscribe” unconditionally to the Lutheran Confessions because they are a pure exposition of the Word of God. This is the way our pastors, and every layman who confesses his belief in the Small Catechism, is able with great joy and without reservation or qualification to say what it is that he believes to be the truth of God’s Word.

Dr. C. F. W. Walther, the Missouri Synod’s first president, explained the meaning of an unconditional confessional subscription in words as clear and poignant today as they were then:

An unconditional subscription is the solemn declaration which the individual who wants to serve the church makes under oath that he accepts the doctrinal content of our Lutheran Confessions, because he recognizes the fact that they are in full agreement with Scripture and do not militate against Scripture in any point, whether the point be of major or minor importance; and that he therefore heartily believes in this divine truth and is determined to preach this doctrine.