In The Holiness of God, R.C. Sproul calls this "Luther's own private Gethsemane."
O God, Almighty God everlasting! how dreadful is the world! behold how its mouth opens to swallow me up, and how small is my faith in Thee!… Oh! the weakness of the flesh, and the power of Satan! If I am to depend upon any strength of this world – all is over… The knell is struck… Sentence is gone forth… O God! O God! O thou, my God! help me against the wisdom of this world. Do this, I beseech thee; thou shouldst do this… by thy own mighty power… The work is not mine, but Thine. I have no business here… I have nothing to contend for with these great men of the world! I would gladly pass my days in happiness and peace. But the cause is Thine… And it is righteous and everlasting! O Lord! help me! O faithful and unchangeable God! I lean not upon man. It were vain! Whatever is of man is tottering, whatever proceeds from him must fail. My God! my God! dost thou not hear? My God! art thou no longer living? Nay, thou canst not die. Thou dost but hide Thyself. Thou hast chosen me for this work. I know it!… Therefore, O God, accomplish thine own will! Forsake me not, for the sake of thy well-beloved Son, Jesus Christ, my defence, my buckler, and my stronghold.
Lord – where art thou?… My God, where art thou?… Come! I pray thee, I am ready… Behold me prepared to lay down my life for thy truth… suffering like a lamb. For the cause is holy. It is thine own!… I will not let thee go! no, nor yet for all eternity! And though the world should be thronged with devils – and this body, which is the work of thine hands, should be cast forth, trodden under foot, cut in pieces,… consumed to ashes, my soul is thine. Yes, I have thine own word to assure me of it. My soul belongs to thee, and will abide with thee forever! Amen! O God send help!… Amen!