To a large extent, due to the process of reform.
Then you can give examples of where it reflects moral standards (I would use no fault divorces, increased recognition of alternative families arrangements, domestic violence laws etc, and how they have changed over time to reflect changing values.)
Then maybe go to areas where there has been some controversy. Like same sex marriage etc, but say that while federal law is lagging behind state law isn't to the same degree.
I don't know if any of that makes any sense at all, but I hope I have helped a bit.