Marriage is not something that humans invented. It is something that we have been given and from our first days have responded to with respect. We have always understood it to be something that is both exclusive and unique between one male and one female. Rare is the exception to this. In our day, the culture has seen a need to redefine an ageless institution that is at the benefit of all of society. Marriage is a basic good of human life and a natural universal human institution. It is a part of who we are and is not something we can change or manufacture. This is the reason the Church wants to defend marriage--the Church is defending the truth of what God has given us and is striving to protect it from being changed or redefined. Marriage is a relationship of total self-gift and loving trust capable of bringing new life into the world; in other words it is faithful (exclusive to one other), fruitful (open to bringing new life into the world through the couple's love), and permanent (until death).
Your 'Yes' vote this November is a crucial piece in supporting marriage in this state from being changed on the next whim of the culture.
Click on these links below for even more information:
US Bishop's website on Marriage
Minnesota Catholic Conference on Marriage