Why must all revenue bills originate in the house of representatives?

Article I, Section 7 states that all revenue bills shall originate in the House of Representatives but the Senate may propose or concur with Amendments as on any other bills. The reason for this is that at the time the Constitution was written, it was felt that Senators would be more wealthy than Representatives and might be willing to spend more government money than the Representatives would. Also, the House with its greater numbers was seen as being the better guage of the wishes of the people for spending measures.

Revenue bills were only to originate in the House because members of the House of Representatives are the only federal officials elected directly by the people. Senators, up until the ratification of the 17th Amendment in 1913, were chosen by the state legislatures. And the president was chosen by the Electoral College. At the Constitutional Convention in Philadelphia in 1787 it was felt that, in order for the new federal government to have sufficient legitimacy to gain popular support, it was imperative that at least part of the government would always have a popular mandate. Hence the three words at the beginning of the Constitution are "We the People." This meant that the new government would derive its authority directly from the people and not from state governments.