Matthew 17 (v)

When the holy martyrs went to their death in the name of Christ, they were fortified by the Word alone rather than by the appearance of angels. Why don't we stand by the same Word and content ourselves with this alone? We have enough clear, bright and beautiful manifestations with baptism, the Last Supper, the Keys to the Kingdom and the ministry. The ministry of preaching is equal to, nay superior to every angelic manifestation. In comparison, Abraham himself was vouchsafed only a few crumbs and droplets. This is why I pay little heed to the angels. (...) For the divine promise has now been abundantly fulfilled and revealed in Christ. He has bequeathed me His Word to invigorate and edify me. And so I need no longer care that He is so inconstant and fickle and that first this teaching and then another can be derived from the same source.

The complete Luther - "A Meditation for Each Day of the Year" is available as a biligual (English and German) BREVIARY published by Wartburg Verlag Weimar. It can be purchased in English, world-wide from most internet book shops.