The church cantatas of J. S. Bach were designed, composed, and performed to enhance and interpret the message of the Bible to worshippers in the congregations which Bach served. The Lutheran Church of 18th-century Germany appointed specific biblical texts to be read each Sunday and festival day of the year. This series of appointed readings, one from the New Testament letters and the other from one of the four gospels, was the lectionary. The lectionary readings determined the day's theme for the sermon, hymns, organ music, and the cantata. Although Bach clearly indicated the occasion on which most of his cantatas were performed, the readings, and therefore the theme of the day, do not necessarily coincide with the readings and themes of the modern church. The Revised Common Lectionary, in widespread use today among churches in North America, appoints three readings for each Sunday, rotating them in a three-year cycle. For that reason, Bach Through the Year has reassigned the cantatas, as well as the motets, passions, and oratorios, to the Sundays and festivals with whose current readings and themes they most closely correspond. In each commentary, the relationship between a lectionary reading, usually the gospel, and the designated cantata is highlighted. JOHN S. SETTERLUND is an ordained minister of the Evangelical Lutheran Church in America, now retired. He has served as pastor of congregations in South Dakota and Illinois, and as campus pastor at the University of Illinois. A graduate of Luther Theological Seminary, he studied also at Wartburg Theological Seminary under Gordon W. Lathrop and Bach scholar Reuben G. Pirner. Bach Through the Year actually began during the 1985 Bach tercentenary, when the first complete recorded set of Bach's church cantatas was published. Subsequently, alternatives were selected, commentaries written, and adjustments made according to minor changes in the lectionary and the hymnal; finally, listings were added to correlate with the lectionaries of the Lutheran Service Book and Christian Worship: A Lutheran Hymnal, as well as Evangelical Lutheran Worship.