It may be that no scholarly monograph can do justice to the enduring value of Bach’s work as a whole or the full scope of its relationship to the belief system in which it is grounded. This book attempts to focus on one aspect of that work as a kind of microcosm on the nature of Bach’s interaction with the Lutheran Christian theological tradition, with particular reference to one of that tradition’s most characteristic topics. . .
Foremost among the works in question are the “St. John Passion” (composed and first performed in 1724, then re-performed, with significant changes, in 1725) and the Easter and post-Easter cantatas of 1725. In spring, 1724, Bach probed the meaning of John’s account of the Passion to a truly extraordinary degree, producing a setting that remains a milestone to this day. . .a significant number of [the] cantatas [composed for the 1723-1724 liturgical year]. . .feature a quality that relates directly to the “St. John Passion” and might well have awakened Bach’s interest in exploring the meaning of John’s Passion account in the manner that he did: they begin with biblical excerpts (“dicta”), often drawn from the psalms, that their subsequent movements expound upon in a systematic and sequential manner. In many of those cantatas, Bach’s interest in the interpretation of Scripture through musical means is prominent, perhaps stimulating him to create a Passion setting on the same basis.
From: J. S. Bach’s Johannine Theology: The “St. John Passion” and the Cantatas for Spring 1725 by Eric Chafe (Oxford: Oxford University Press, 2014), pp. 4, 5.