Final answer:
The Constitution addresses the legislative branch first in Article I because it's the main lawmaking body, and it's the longest article due to the detailed framework required to establish and organize Congress's bicameral structure.
Step-by-step explanation:
The Constitution deals with the legislative branch in its very first article because it is the primary body responsible for making laws. Article I of the Constitution is the longest because it lays out the framework for how legislation will be crafted, debated, and passed in the United States. It is essential to understand that the creation of a bicameral legislature, with both the Senate and the House of Representatives, was a significant compromise that balanced the power between states and the people. This design was to prevent any single entity from gaining too much power and to ensure a fair representation of both populous and smaller states in the lawmaking process.