Why was representation the first major issue facing the delegates

The main issue of representation centered around large states who wanted representation to be proportional to population and the small states who wanted a set number of representatives that was the same for every state. If this issue wasn't resolved, there would be no agreement and the Union would be doomed. The Great Compromise was the deal struck to prevent that. It stated that the lower House of Congress, the House of Representatives, would have proportional representation and the Upper House, the Senate would have two reps for every state. Representation was the first issue discussed because it was the disputed part of the first plan proposed, the Virginian Plan. The undisputed part detailed the branches of the government.