During the Reformation, a major dispute between the Reformed and the Lutherans was over the doctrine of baptism.
In this matter, Lutheranism did not take the Reformation far enough; while the Reformed understood that water baptism does not save, the Lutherans did not shake off the popish heresy of baptismal regeneration.
Thus for the two camps there were irreconcilable differences. As one author writes,
Lutherans accused Calvinists of having turned the sacrament into a mere sign and empty symbol; the Reformed retorted that the Lutheran understanding amounted to a Catholic view of the sacrament.
At the Colloquy of Montbéliard in 1586 the Reformed theologian Theodore Beza debated the Lutheran Jakob Andreae about several doctrinal differences, including baptism.
Championing the Reformed view of baptism, Beza noted the antithesis between the Reformed and the Lutherans:
The quarrel between you and us is whether holy baptism is a bath of rebirth and a renewal in the Holy Spirit [Lutheran view], or whether it is simply a sign that signifies and seals our filial relationship to God [Reformed view].
Author Jill Raitt writes the following summary of some of Beza's arguments against Lutheran baptism at the Colloquy of Montbéliard:
Beza said that it is idolatrous to ascribe any latent power to any water, even sacramental water. God does not transfer divine power absolutely to any created thing. ... Beza argued that salvation depends not on baptism but on one's faith.
Beza, in short, rightfully saw baptismal regeneration as an idol, and that this doctrine is contrary to the doctrine of salvation by Christ through faith alone.
 Bobo Nischan, Prince, People, and Confession: The Second Reformation in Brandenburg (Philadelphia, PA: University of Pennsylvania Press, 1994), 142.
 Acta Colloquii Montis Belligartensis (Tübingen, 1587), 758. Cited in Ibid., 141, 142.
 Jill Raitt, The Colloquy of Montbéliard: Religion and Politics in the Sixteenth Century (New York, NY: Oxford University Press, 1993), 138.