Colossians 3:18-19 (ESV)
Rules for Christian Households
 Wives, submit to your husbands, as is fitting in the Lord.  Husbands, love your wives, and do not be harsh with them.
Colossians 3:18-4:1 addresses three household relationships: Wife/Husband, Child/Parent, Slave/Master. In the Greek household it was not unusual to have multiple generations under one roof. It was also common to consider the slaves as part of the household. Often Greek teachers, including Aristotle, addressed these three areas of household relationships. What was not common was for those teachers to address both sides of those relationships. They would teach about the wife's responsibility to submit to her husband, but they would not address the husband. In their culture he had the right to do whatever he wanted. The same was true of Children/Parents and Slave/Master. The Greek teachers would explain the importance and necessity of obedience on the part of the children and slaves, but fathers and masters were the absolute lords of their homes. Further, while the importance of slaves obeying was taught, slaves were never directly addressed by the teachers. What Paul does by addressing slaves directly and by explaining the responsibilities of husbands, fathers and masters is incredibly cross-grain to his culture.
It is not uncommon to hear that these verses are reflecting a first century culture, but the truth is that in those days you would never hear that a husband should not be harsh with his wife, a parent should not provoke their children to anger or discourage them or that a master should treat his slaves justly and equitably. That was brand new. It did not come from their culture. Christianity brought an equality to all people that was to be demonstrated in gentleness, understanding, justice and equitable treatment no matter what your role or responsibility in life. That was new and it changed the world.
Why do women have the right to vote? Why did England and the USA eventually outlaw slavery? Why were child labor laws established? Why did our country decide early on that children should be educated no matter what station in life they came from? Yes, a lot of bad things have been done in history in the name of Christianity, but it was the truth and influence of Christianity that brought about every one of these things. Christians truly believe that we all stand on level ground before God. These verses are written in the context of verse 11.
Colossians 3:11 (ESV)
 Here there is not Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave, free; but Christ is all, and in all.
We all have different roles and responsibilities, but as believers we are first brothers and sisters in Christ. We are secondly wives, husbands, children, parents, slaves and masters. Those relationships are different from the world precisely because of our mutual connection to Christ. May that be reflected in all that we do.
By His grace,