In their day it was simple. Each state sent two of its own to the Senate to represent them. They also sent a number of Representatives to the House of that name based on the population within each state. The more people, the more representatives. Hence the enumeration. Simple.
Today the census is a racket. It doesn't just count people, it manipulates the count to ensure that pockets of people who routinely vote for the polecats in power are higher while opposition voters are counted lower. Then, Congressional and local legislative districts are gerrymandered, which means drawing lines on maps to create areas guaranteed to vote for You while chopping up neighborhoods that usually vote for Them.