Uh, okay.
How about this: The Articles of Confederation acted on the states. The states sent delegates to Congress. Perfect sense.
The Constitution acts on both the people and the states. Both had representation in Congress. Perfect sense.
In fact, a draft Constitution without state representation would have been a dead letter at the state ratifying conventions.
What is the logic of two popularly elected lawmaking houses? None.
For that matter, a republican constitution of government that acts on entities not represented at the law-making table has a name: Tyrannical.
One House is apportioned by population. The other gives each state equal representation. One answers to rural and agricultural interests, and the other to urban interests. There’s your logic. Senators usuallly have to answer to a larger electorate than representatives. Also, it’s easier for nutjobs to become representatives than senators.