Steve:
Imagine this.
We go back to everyone owning their own little plot of land, and using it to grow vegetables (and if they're very lucky to fatten livestock).
If they can't provide for their families just from this, and from trading food for services that they require (work on their habitations, etc.) They will probably end up using someone (further up the 'food chain') to arrange a 'fair' method of exchanging what they can produce for what they need to buy.
Allowing for this intermediary to make some sort of a living from this eventually you'll get a system where those who produce foodstuffs and are providing goods to those who can't, need a middle-man arranging the dealings, and taking a cut.
Eventually the middle-man will expand what he's doing and make a small profit from everyone who he is helping to deal 'what they have' for 'what they want' as people with a product to sell don't always want something that their prospective buyers want to exchange.

Just swap the 'government' or 'the royal family' for the 'middle man'.