Money is a convenient tool for bartering. It's a lot easier to carry money in ones pocket than say, a cow, a bushel of apples or a barrel of oil.
There will always be some sort of money. as every person can't do everything; each person has different skills. For example, one person can sing really good, but they cant grow a plant (black thumb). So they trade their songs for things they need to survive (food, shelter). NOw that person could sing every time they wanted something (provided there was a person willing to trade what they had for a song or they weren't sick and unable to sing), or they could give a concert and charge money to those who wished to attend, and use that money later to secure (purchase) their necessities.
If there was no money then what would be the root of all Evil? Oh, I know. Light Mayo, because that stuff is just wrong. True evil knows no bounds. Besides we all need money for Lollipops.
Well, you need it to buy stuff and if you wanna benefit from society, you have to contribute in some way and you get money in return for contributing. It's a lot easier than bartering, too. Life would probably be more difficult if not for some form of money and it would probably go back to bashing each other over the head to obtain food and goods and all that fun stuff.
Benedict Arnold 