Ephesians 6:9

Masters, do the same to them, and stop your threatening, knowing that he who is both their Master and yours is in heaven, and that there is no partiality with him.

Ephesians 6:9

Now, what was applied to slaves is being applied to masters.  It's actually the same thing.  Yes, slaves are in different positions compared to masters.  However, as slaves are treat their masters well, working hard for them, masters are to deal kindly with their slaves.  Because slaves are in subjection to masters, the temptation for masters to deal harshly with their slaves.  However, they are to stop threatening and abusive words towards their slaves.  An important thing to keep in mind is that God is master of both slaves and masters.  If you, a master, deal harshly with your own slaves, how would God deal with you?  God will not treat you differently just because you're a master and not a slave.  For God, there is no partiality.