John Calvin's plan to study Exodus, Leviticus, Numbers, and Deuteronomy in the form of a Harmony was conceived in the congrégations, the Bible studies of the ministers of Geneva and its surrounding villages. A surviving manuscript of Calvin's introductory exposition to the series, studied here for the first time since the sixteenth century, reveals intriguing details on the conception of this plan. It also sheds light on the history of the congrégations, this fascinating example of concentration on the Bible in Geneva, on the co-operation of the ministers, and on Calvin's role as the Moderator of the Company of Pastors. The origin of the Harmony idea is an adaptation of the Gospel Harmonies. Calvin's approach is highly original in the history of exegesis. The text of the congrégation points to Calvin's reading of the commentaries of the Lutheran scholars Martin Borrhaus and, possibly, Johannes Brenz.