How to Build Better Relationships
In first-century Greco-Roman society, fathers—as the head of the household—had complete authority within the household to administer discipline. Paul advises them to avoid exercising that authority in ways that might cause their children to harbor resentment. Paul is advocating for fathers treating their children with kindness, which would have been unexpected for Graeco-Roman society; he is arguing that parents treat their children as Christ would.
For Paul to say that they needed to treat their children as human beings and consider their feelings was revolutionary.
In Graeco-Roman society, masters had the right to treat slaves as they saw fit. Paul commands masters to set aside their rights and to instead treat their slaves with kindness as people who are equal before Christ (compare note on Eph 6:5).