Eph 6:9 And you, masters, do the same things to them, giving up threatening, knowing that your own Master also is in heaven, and there is no partiality with Him.
Paul addresses masters last with a charge to them to lead wisely and with humility. Since master’s position can be abused to belittle or threaten those underneath them, Paul cautions masters to examine how they handle those they lead. Paul further states that masters also have a greater master over them. Masters should act correspondingly toward servants/slaves, as if the eye of Christ were on them, which indeed it is.
Masters must put themselves in the place of their servants, and act towards them as they would desire to be treated if their positions were reversed. It is a practical application of the great rule of behaving with gentleness and humanity, not in a harsh or domineering way.
There must be mutual good will and mutual service that there may be peace and unity. “If both masters and servants would consider their relation and obligation to God and the account they must shortly give to Him, they would be more careful of their duty to each other. Thus the apostle concludes his exhortation to relative duties.“ Matthew Henry