What is the purpose of republican government?

Everything. For starters you have individual and civil rights that are protected. You elect your officials, so if you don't like what they are doing, you can vote them out. (Personally, they should be voted out and changed often). You basically have the right to do anything you choose to do, as long as you aren't hurting anyone, stealing anything, or vandalizing any property. The Word Republic comes from two Greek Words. Res, which means Thing, and Publica, which means The Public. Therefore, Republic means the Public Thing, The Law.

You also have a Free Market economy, in which you may make a profit. Free Market also benefits the consumer because the producers will compete (usually by lowering prices) so that the consumer will purchase from them.

One gigantic problem with our Free market Republic is that our corporations have literally tilted the table and turned us from Free Market Capitalism to Corporatism (Crony Capitalism). This is why Wall Street gets all of the benefits and bailouts, while we the people foot the bill.