Why would a small state be more powerful if representation was numerically equal per state?

The issue of representation in the U.S. Congress was hotly debated at the Constitutional Convention in 1787. The Convention was originally called to revise the Articles of Confederation, which had been the government of the original 13 colonies of the United States during and after the American Revolution. Leaders such as Benjamin Franklin feared the government under the Articles was too weak, and so they met to revise, and ultimately replace, the Articles with a stronger U.S. government, creating the Constitution.
One of the biggest issues that emerged in creating a new government was state representation in the national Congress. Large states supported the Virginia Plan, which advocated replacing the Articles with a stronger national government and basing a state's representation in Congress on the population of that state. Smaller states, such as Rhode Island and New Jersey, opposed this plan because it gave more representation, and therefore more power, to larger states. The higher a state's population, the more representatives they would be able to send to Congress, and thus the more votes they would have in Congress.
Smaller states therefore preferred the New Jersey Plan, which called for equal representation in Congress—every state would get the same number of representatives in Congress. This plan would mean that a smaller, less populous state, such as Delaware, would have the same number of votes, and therefore the same influence, as a larger state like New York or Virginia.
In the end, the Great Compromise helped settle the dispute and created the bicameral (two house) Congress we have today. Representation in the lower chamber of Congress, known as the House of Representatives, is based on each state's population. The upper chamber, called the Senate, allows every state to send the same number of representatives: 2 senators per state for a total of 100 senators.