The Federalist Papers are a series of articles, written by several key founders under the pseudonym “publius”, intended to persuade the colonies to ratify the Constitution. These articles tell us a great deal about what the founders were really thinking when they wrote the Constitution, and how to interpret it today.
Since the Constitution is still the official specification for the United States government, and is still the binding contract between the US government and We the People, it makes a great deal of sense to understand what the designers were thinking, and what the several states agreed to, when they ratified the Constitution. What they agreed to, except where later amended, is still the official law of the land today. We are justified in demanding that our government live up to that agreement in full.