Hello.
The Great desideratrum Madison refers to sacrifice self-interest for the common good.
"Desideratum" is a Latin word meaning "thing to be desired."
And he's saying that the most important thing about a government is that it be designed in such a way that it (1) doesn't unfairly favor one interest group over another, and (2) doesn't exercise power for its own sake, to make itself more powerful and rich at the expense of society as a whole.
Have a nice day
