The more I read about the Reformation, the more I am interested in what I would call the second-generation Reformed ecumenism. The Reformed and Lutheran camps were at odds in the first generation between Zwingli and Luther, but second generation reformers John Calvin, Phillip Melancthon, Thomas Cranmer, Martin Bucer and Bullinger all made moves towards uniting the Reformed, Lutheran and Anglican streams in one Reformation confession. Often the starting point was the Augsburg Confession, especially as explained by Melancthon. Tragically, the more ardent Lutherans rejected Melancthon's efforts as compromise and liberalism, the Church of England went from the golden age of Protestantism under Edward VI to the brutal rule of Catholic Bloody Mary in which Cranmer was burned at the stake, and so reconciliation was thwarted, despite its Biblical mandate.
I recently encountered an interesting article online I thought I would recommend. It is not a published article, but most of the article consists of cited quotations of documents and correspondence. It highlights the efforts of John Calvin towards unity, but this was not at the expense of purity, as the author concludes:
"For Calvin the fundamental criterion for unity was pure doctrine."