"The Church, indeed, consists of men, each of whom as a citizen of an earthly kingdom is called upon to do his political duties, as well as his other duties in the name of the Lord Jesus. For ordinary purposes in ordinary life, it may not be important, or even perhaps possible, for a man to distinguish that which is incumbent on him as a citizen of an earthly realm from that which is incumbent upon him as a child in the family of God.
But the distinction is of vast importance in regard to those who are called to office and ministry in Christ’s Church. The terms of their commission lay down the limits of what they are to do by Christ’s authority; they have no commission to put the affairs of society right, or to eradicate the evils in this present naughty world. In the Gospel of the grace of God, they have committed to them the supreme means of touching men personally and inspiring them with high but practical ideals. This is the grandest work to which any man can give himself; and it is a miserable thing if he fails to put his best energies into this task, and prefers instead to compete with journalists and politicians in guiding some project for social reform.
It is to forsake the fountain of life and to strain at accomplishing some apparent improvement by taking up implements that are less certain and less effective, even for securing human welfare, than the means of grace instituted by Christ Himself… Christ sent His apostles on evangelistic work and bade them administer the sacraments and exercise pastoral care; but He did not enjoin them to agitate for social reforms."
Johann Michael Reu, Homiletics