The role of money

There is no single answer for it. But one of the answers is that in our world money shows the value of a person, company, or country. The more money you have - the more valuable you are. It's not like it should be, it's not like it was "designed". But it's how things really are. 

It's completely fine when you're producing goods that you exchange for money. You create value - you're valuable. 

But there are plenty of cases when it doesn't work like that. There are legal and illegal ways to get more money than the value you bring. You can even bring damage to others, make money and it still is legal. I think everyone can make up a couple of such cases without thinking for a long time. 

Roles of money we REALLY need

Reward

One of the roles money plays in our society is a reward role. When someone does something useful for others, nobody argues that such action has to be rewarded. 

Money solves this problem... partially.  When we exchange some limited goods (mostly, physical) for money it's completely fine, and (almost) nobody thinks it works wrong. Sometimes people still think reward distribution is wrong because of big-corpo stuff, but it's another topic.  

The weak point of money shows up when we're talking about the low or near-zero cost of production and intellectual property (that has a near-zero cost of creation of copy). We have a dilemma. If you want to be rewarded, you need to take money from other people. Higher the price - more money you've got. But fewer people would have access to the goods you produce. 

Access limitation

The second role of money is an access limitation. When you produce something, often the demand can be much higher than production capacity. In this case, money solves the problem of deciding who will get priority access.