The correct answer to this open question is the following.
The main idea or argument of the MASSVote source and the information it contains is the following.
One of the rights and obligations to all United States citizens in to vote in order to elect the President of the United States, their respective state governors, and their representatives in Congress.
Well, MASSVote source is a site that aims to invite American people to participate in elections. To accomplish that, the site clearly explains the reasons why people should actively participate in elections. The site says that the cornerstone of American democracy is based on people´s participation, although not all people participate.
The site offers explanations that invite people to reflect on the importance of elections and how people can influence the life and direction of American democracy. It has enough resources so people could learn new things, stay informed, and have a clear purpose to vote in the next election.