Charles Hodge on Ephesians 6:7

V. 7. The whole character of the obedience of the slave is summed up in this verse, δουλεύοντες, ὡς τῷ Κυρίῳ καὶ οὐκ ἀνθρώποις, doing service, to the Lord and not to men. This, as the Scriptures teach, is not peculiar to the obedience of the slave to his master, but applies to all other cases in which obedience is required from one man to another. It applies to children in relation to their parents, wives to husbands, people to magistrates. Those invested with lawful authority are the representatives of God. The powers (i. e. those invested with authority) are ordained by God; and therefore all obedience rendered to them out of regard to his will, is obedience to Him. And as obedience to God is rendered to one infinitely true and good, it is even more elevating than obedience to truth and goodness. Foreign as all this is to the proud and rebellious heart of man, which spurns all superiority and authority, it is daily illustrated by the cheerful and patient submission of the people of God even to the capricious and unreasonable exercise of the authority of those to whom God has placed them in subjection. It is to be remarked that the apostle presents this principle not merely in a religious, but a Christian form. We are required to do service, as to the Lord, and not to men. It is to Christ, God manifested in the flesh; to him, who being in the form of God, thought it no robbery to be equal with God, but humbled himself, taking on him the condition of a slave, μορφὴν δούλου λαβών; it is to this infinitely exalted and infinitely condescending Saviour, who came not to be served, but to serve, that the obedience of every Christian, whether servant, child, wife, or subject, is really and consciously rendered. Thus the most galling yoke is made easy, and the heaviest burden light.

The words μετ᾽ εὐνοίας qualify δουλευόντες, with a willing mind doing service. This stands opposed to the sullenness and inward indignation with which a service extorted by fear of punishment is often rendered. No service rendered to Christ can be of that character. It is rendered with alacrity and cheerfulness.