Ephesians 6:5

Masters according to the flesh; persons to whom you justly owe service, or who by human laws have power to force you to serve them. Obey their commands whenever you can do it without disobeying the commands of your Master in heaven.

With fear and trembling; reverentially, and with that fear of God which is the beginning of wisdom, and which shall make you anxious to please him.

As unto Christ; for the purpose of honoring him and promoting his cause.