“What, then, is the office or work of the ministry of the church?  Sirach says, 38:25-26: ‘The wisdom of a scribe (namely for the kingdom of heaven) requires opportunity for leisure; and it is necessary for him to be free of other matters, who wants either to obtain that wisdom for himself or impart it to others.  For how can he deal with wisdom, who must hold the plow and drive oxen, etc.?’  The office of a minister of the church therefore is, that he diligently study the holy Scriptures and give himself to reading them (1 Ti 4:13), moreover, that he labor in the Word and doctrine (1 Ti 5:17), that he feed the flock of Christ and the Church of God (1 Ptr 5:2; Acts 20:28), that is, he is to serve the church with the preaching of the Word and administration of the Sacraments and the use of the keys.  As Origen aptly writes on Lv 8: ‘These two are works of a priest: First, that he learn of God, by reading the Holy Scriptures and frequent meditation, and that he teach the people, but that he teach the things that he himself has learned form God.  There is also another work, which Moses does: he does not go to war, but prays for the people, etc.’”

Chemnitz, Martin.  Ministry, Word and Sacraments: An Enchiridion, 1593.  Edited, translated, and briefly annotated by Luther Poellot.  2007, St. Louis: Concordia Publishing House, 38 §33.