Ephesians 6:9

And masters, treat your slaves in the same way. Do not threaten them, since you know that he who is both their Master and yours is in heaven, and there is no favoritism with him.

(v9, NIV)

The last few verses have just finished talking about slaves. In the last verse, Paul mentions that as slaves, we serve wholehearted as serving the Lord because the Lord will reward everyone for whatever good he does. This is the way in which the Lord treats everyone. So here in verse 9, when masters are instructed to treat their slaves in the same way, this "same way" is referring to the way in which God treats each and every one of us. We are all in subjection to God; similarly, slaves are in subjection to their masters. So, masters should treat their slaves in the same way.

Masters, be careful how you treat your slaves. Remember that God is master to both slaves and free. God is over and above those who are masters and those who are slaves. As a master, you are not the ultimate authority. You too are in subjection at least to God. If you treat your slave or slaves harshly, how do you expect God to treat you? God will not favor you for any arbitrary difference between you and others. God will not favor you because you are wiser or richer or better looking than someone else. He will show no favoritism, so do not hope for that.