The major difference between Luther and Calvin had been the issue of predestination. Luther had argued that salvation came from faith alone; that good works were not necessary and that salvation was available to all. Faith reconciled one to God. Calvin believed that God had all men were depraved sinners who deserved God's judgement; but God had determined from the beginning of the world that certain persons had been "predestined" to be saved:

Predestination we call the eternal decree of God by which He determined in Himself what would have to become of every individual of mankind. For they are not all created with a similar destiny; but eternal life is foreordained for some and eternal damnation for others. Every person, therefore, being created for one or the other of these two ends, we say is predestined to life or to death.

 Calvin and Luther also disagreed over the significance of Holy Communion. Luther held firm to the theory of transubstantiation; that is the bread and wine were transformed into the actual body and blood of Christ. In fact, when a meeting was held between Luther and Ulrich Zwingli in an attempt to resolve religious differences, Luther struck the table with his fist before storming out of the room shouting Hoc Est Mea Corpus! ("this is my body.") Calvin argued that there was a something of a spiritual presence of Christ at the Communion. Salvation and the communion host were so closely related that one could:

“easily pass from one to the other. For why should the Lord put in your hand the symbol of his body unless it was to assure you that you really participate in it?”

What are the differences between Martin Luther and John Calvin?

There were many differences between the two great titans of the Reformation. Some were related to their respective temperaments; others to their political and geographical circumstances. Broadly speaking, one could say that Luther was the founding spirit of the Reformation whereas it was Calvin who systematically set about formulating a coherent Protestant doctrine. Calvin was also much more minutely concerned with ecclesiastical matters, with the hard practical work of building a new church to stand as an immovable rock against the immense spiritual and temporal power of Rome.

Specifically, this leads us onto one of the most significant differences between Luther and Calvin: their understanding of the relations between church and state. Luther, in essence, believed they should be completely separate. The state had the God-given task of ensuring peace and stability in society; the church was concerned with the salvation of souls. Luther favored a strong state capable of preventing mass outbreaks of anarchy and defending private property against ravaging hordes of peasants. But the state also had the right to regulate religious affairs. Indeed, one could say that for Luther the church was strictly subordinate to the state in this regard.

There is little doubt that Luther was strongly influenced by two factors here. Firstly, he was reacting against what he saw as the persistent interference of the Catholic Church in secular affairs. One of the reasons why the Reformation caught fire so quickly in Germany is that there was widespread resentment at the increasing amount of money sent to Rome either in the form of taxes or proceeds from the sale of indulgences.

Secondly, the political organization of what we would now call Germany consisted of a patchwork quilt of different forms of government. The most common of these, and the one operating in Luther's native Saxony, was the princedom. It was perfectly natural, then, for Luther to accord great secular power to the reigning monarch, not least because he was a major beneficiary of such power.

Luther believed that there was no sense in the state Christianizing society, as it were. Calvin, however, looked at the matter differently. In Geneva, he was instrumental in establishing the Consistory, a kind of Church Synod. The role of the Consistory in Genevan public life was hugely influential. Its main task was to impose religious discipline and, if necessary, punish those who strayed too far from the tenets of the Reformed faith. Its increasingly dominant place in public life also frequently led to regular outbreaks of Puritanical zeal with taverns closed, sports disrupted, and card tables overturned by the Consistory's enforcers.

While it's not correct, strictly speaking, to describe Calvin's Geneva as a theocracy, there is no doubt that the Reformed Church did enjoy a considerable degree of autonomy, certainly one that would have been unthinkable for a Lutheran church. Calvin jealously guarded the right of the Church to excommunicate what it regarded as sinners and apostates. This placed the Church in regular conflict with Geneva's government, the Council of 60, who explicitly denied them this right. However, the Church continued to carry out excommunications in open defiance of the Council in keeping with Calvin's elevated conception of what a Reformed church should be.

Both Luther and Calvin came to their positions from intense personal inner struggle. Both had originally been clerics of the Catholic Church; Luther had been a German professor, Calvin a French lawyer and humanist. Luther's writings were in response to the corruption that was prevalent in the Catholic Church, primarily the sale of indulgences; Calvin responded to his own inner conviction of the utter depravity of man.

Luther said that salvation comes from faith alone; the Pope had no special authority; rather he spoke of the "priesthood of all believers." Luther argued that there were only three sacraments as opposed to the seven practiced by the church; those in which Jesus actually participated while on earth.

Calvin frequently spoke of the “abyss” over which mankind hovered. The most important element of his theology was the doctrine of predestination. Calvin wrote that God was sublime, and so overwhelming and awe-inspiring that human beings were insignificant, sinful, and unworthy. Yet God was also a God of love, who planned from the beginning of the universe to the end of time, and selected some human beings, the “elect,” for salvation; others were selected for damnation. The following quote is from Calvin:

Predestination we call the eternal decree of God by which He determined in Himself what would have to become of every individual of mankind. For they are not all created with a similar destiny; but eternal life is foreordained for some and eternal damnation for others. Every person, therefore, being created for one or the other of these two ends, we say is predestined to life or to death.

Predestination was the area in which Luther and Calvin disagreed most. Where Luther had emphasized reconciliation to God through faith, Calvin emphasized obedience to His will. Calvin’s position on the Eucharist also differed with Luther. He argued that there was a “spiritual” presence. There was such a close connection between the communion host and the gift of salvation which it symbolizes that one can

“easily pass from one to the other. For why should the Lord put in your hand the symbol of his body unless it was to assure you that you really participate in it?”

Luther's teaching was of consubstantiation: Christ was present at the Eucharist, but the bread and wine were not transformed, as had been taught by the Catholic Church.