Servants, be obedient to them that are your masters according to the flesh, with fear and trembling, in singleness of your heart, as unto Christ; (...). And, ye masters, do the same things unto them, forbearing threatening: knowing that your Master also is in heaven; neither is there respect of persons with him.
Ephesians 6 (v and ix)
If you have received a gift from God that makes you more powerful, more exalted, nobler and more learned than other people, then remember that He has commanded you to serve others with your gift. Be aware that a poor shepherd boy may be nothing compared with you whereas he could be far greater in the sight of God and His angels and could be lifted up to heaven whereas you in all your splendour, majesty, glory and in all your jewels will be cast down to hell. Before God everything is equal. (...) At the same time, even though people are equal before God and have in common: one Lord, one Faith, one Baptism, - it is evil and completely out of order if a ploughboy at his plough or the scullery maid in the kitchen get on their high horse and say to their masters or mistresses: "Before God, I am just as noble and good as you so I neither need to be in your service nor should I obey you." (...) This is totally unbefitting for a Christian and is totally contrary to the Law and teaching of Christ.
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.