The Federalist Papers, written by James Madison, John Jay and Alexander Hamilton, is the document most frequently referred to when trying to get a feel for the original intent of the framers of the Constitution. One such intention is found in Federalist 56 where Madison says, "...it seems to give the fullest assurance, that a representative for every thirty thousand inhabitants will render the (House of Representatives) both a safe and competent guardian of the interests which will be confided to it."
Excellent research, shows that in 1804 each representative represented about 40,000 people. Today, each representative represents close to 700,000. If we lived up to the vision of our founders, given today's population, we would have about 7,500 congressmen in the House of Representatives. It turns out that in 1929 Congress passed a bill fixing the number of representatives at 435. Prior to that, the number of congressional districts was increased every 10 years, from 1790 to 1910, except one, after a population census was taken.
We might ask what's so sacrosanct about 435 representatives? Why not 600, or 1,000, or 7,500? Here's part of the answer and, by the way, I never cease to be amazed by the insight and wisdom of our founders: James Madison, the acknowledged father of the Constitution, argued that the smaller the House of Representatives relative to the nation's population, the greater is the risk of unethical collusion. He said, "Numerous bodies ... are less subject to venality and corruption. " In a word, he saw competition in the political arena as the best means for protecting our liberties. If Madison were around today to see today's venal and corrupt Congress, he'd probably say, "See, I told you so!"
In addition to venality and corruption, restricting the number of representatives confers significant monopoly power that goes a long way toward explaining the stranglehold the two parties have and the high incumbent success rates. It might also explain the power of vested interest groups to influence congressional decisions. They only have to bribe, cajole or threaten a relatively small number of representatives. Imagine the challenge to a lobbyist, if there were 7,500 representatives, trying to get a majority of 3,813 to vote for this or that special privilege versus having to get only a 218 majority in today's Congress.