In an Advent sermon from 1532 preached at the stadtkirche, Luther noted the difference between the Lord Christ’s kingdom and that of the lord Caesar. Luther said it in Latin: finis politiae est pax mundi; finis ecclesiae est pax aeterna. Here’s his explanation:
“The end purpose of the government is temporal peace, while the ultimate end of the church is not peace and comfort on earth, nice homes, wealth, power, and honor, but everlasting peace. Caesar does not care whether I die a blessed death and come to everlasting life, nor can he be of help against death, but must himself die just like me. Death comes to him as [it does] to the lowly beggar. Caesar’s jurisdiction pertains to this temporal, transitory life; but where this temporal life ceases, there the rule of the Christian church intervenes. Let this be the goal and purpose for which the Christian realm strives and aims: to proclaim the treasure for troubled and anguished consciences which Christ has earned for and committed to his church, namely, the forgiveness of sins and everlasting peace.”
Quotes taken from page 103 of volume 5 of the Baker set of Luther’s sermons. For more info on Luther’s two kingdoms, along with the Lutheran confessions be sure to check out this book - (just released).