There are two sacristy prayers of Luther that circulate. I always wondered which was accurate, or whether they were both apocryphal. So I hunted them down in Luther’s Works.
Curiously, I found it in Luther’s lectures on Genesis.
Lecturing on Genesis 27:11-14, Luther ruminates on the foolishness of Jacob and Rebekah’s deception of Isaac, and how God is faithful in spite of it all. Luther says in LW 5:123, above all a leader in the church should pray in this manner:
Lord God, Thou hast appointed me in the church as bishop and pastor. Thou seest how unfit I am to attend to such a great and difficult office, and if it had not been for Thy help, I would long since have ruined everything. Therefore I call upon Thee.
Of course, I want to put my mouth and heart to use. I shall teach the people, and I myself shall learn and shall meditate diligently on Thy Word. Use me as Thy instrument. Only do not forsake me; for if I am alone, I shall easily destroy everything.
Here is another version. If this is genuine, I would love it if someone would give me a citation from Luther’s Works:
O Lord God, dear Father in heaven, I am indeed unworthy of the office and ministry in which I am to make known Your glory and to nurture and to serve this congregation.
But since You have appointed me to be a pastor and teacher, and the people are in need of the teaching and the instruction, be my helper and let Your holy angels attend to me.
Then if You are pleased to accomplish anything through me, to Your glory and not to mine or to the praise of people, grant me, out of Your pure grace and mercy, a right understanding of Your Word and that I may also diligently perform it.
O Lord Jesus Christ, Son of the living God, shepherd and bishop of our souls, send Your Holy Spirit to work with me to will and to do through Your divine strength according to Your good pleasure. Amen.