The syncretistic controversy was the theological debate focusing on efforts to unite Protestant churches in 17th century Germany.
In regard to Catholicism, he would have (as Melanchthon once would have) conceded to the pope a primacy by human right, rather than divine right; he also stated that one might call the Mass a sacrifice.
In 1650, the dukes of Brunswick responded to the Elector of Saxony, urging that the discord not be allowed to continue and proposing a meeting of the political councillors.
The disagreement arose again in Hesse-Kassel, where Landgrave William VI sought to unite his Lutheran and Reformed subjects, or at least to lessen their mutual hatred.
They drew up a statement which recognised differences of opinion between the parties, but at the same-time showed an agreement between them on all essential matters.
In 1663 in Brandenburg-Prussia, the "Great Elector" Frederick William I forbade preachers to speak of the disputes between the Evangelical bodies.
A long colloquy in Berlin (September 1662 to May 1663) led only to fresh discord and the conferences ended in 1664 with the publication of another "syncretistic" edict.
Any person refusing to sign the form declaring his intention to observe this regulation was deprived of his position, including Paul Gerhardt, a pastor and noted hymnwriter.
The citizens of Berlin petitioned to have him restored and, owing to their repeated requests, an exception was made for him, although his conscience did not allow him to retain a post which, as it appeared to him, could be held only on condition of a tacit repudiation of the Formula of Concord.
Wittenberg found its new champion in Aegidius Strauch, who attacked Calixtus with all the resources of learning: polemics, sophistry, wit, cynicism, and abuse.
The Saxon princes now recognized the danger that the attempt to carry through the "Consensus" as a formula of belief might lead to a fresh schism in the Lutheran Church, and might thus render its position difficult in the face of the Catholics.
The proposals of Calov and his party to continue the refutation and to compel the Brunswick theologians to bind themselves under obligation to the old Lutheran confession therefore remained unimplemented.