Ephesians 6:5

Servants, be obedient to them that are [your] masters
The apostle enlarges on the duty of servants, as well as frequently inculcates it in his epistles; because, generally speaking, they were more rude and ignorant, and less pains were taken with them to instruct them; they were apt to be impatient and weary of the yoke; and scandal was like to arise from servants in the first ages of Christianity through some libertines, and the licentiousness of the false teachers, who insinuated, that servitude was inconsistent with Christian freedom: the persons exhorted are "servants", bond servants, and hired servants; who are to be subject to, and obey their "masters", of each sex, whether male or female, of every condition, whether poor or rich, believers or unbelievers, good or bad humoured, gentle or froward: such as are their masters

according to the flesh;
or "carnal masters", as the Vulgate Latin version renders it; even though they are unregenerate men, and are in a state of nature, and only mind the things of the flesh, yet they are to be obeyed in their lawful commands; or "in things pertaining to the flesh", as the Arabic version renders it; in things temporal, which concern the body, and this temporal life; not in things spiritual and religious, or that belong to conscience, and which are contrary to them: or "according to your flesh", as the Ethiopic version renders it; signifying that they are only masters over their bodies, not their consciences; and that their power only extends to corporeal things, and can last no longer than while they are in the flesh; see ( Job 3:19 ) ; and obedience is to be yielded to them

with fear and trembling;
with great humility and respect, with reverence of them, and giving honour to them, with carefulness not to offend them, with submission to their reproofs and corrections, and with fear of punishment; but more especially with the fear of God, being by that influenced and constrained to obedience;

in singleness of heart;
with readiness and cheerfulness, without hypocrisy and dissimulation, and with all integrity and faithfulness:

as unto Christ;
it being agreeable to his will, and what makes for his glory, and serves to adorn the doctrine of God our Saviour in all things.