Money was simply invented to make it easier to trade stuff and because it was a convenient way of measuring the relative value of different things. Its utility lies in the fact that it facilitates saving, or delaying the consumption of resources from one period to the next, and because it makes it easier for those saved resources to be recycled.
Now there are two great mistakes people make when they're discussing money. The first mistake is to think that it is real and nothing else matters. The second mistake is to think that it isn't real and doesn't matter at all. The trick is to appreciate that whilst money is an abstract concept, behind that abstraction lies something very real.
For example; when, at the end of every month, your employer hands you a cheque (or check), the money value of that cheque might not be 'real', but it represents the very real fact that you have got out of bed most days and dragged your sorry arse (or ass) across town and sat down at a desk, or stood in front of a production line, and actually done something which might possibly have been deemed useful and of value by said employer. Thus when you decide not to spend some of the money value of that cheque and to put it aside for some future eventuality, the accumulated value of those savings might on the face of it appear to be nothing more than a number on a computerised ledger, but in reality it will represent weeks, months, or even years of physical effort on your part.
Should some individual then come along and announce that they have all of a sudden decided to abolish this 'old money' (thus rendering your savings valueless) and replace it with some 'new money', you are unlikely to be satisfied with their explanation that none of it was 'real' in the first place, and that the nation's productive capacity remains intact. You are far more likely to go down to Texas, get yourself an AK47, and then return to shoot the little bastard's head off.
This polemic was brought to you by the Department of Financial Sanity and will probably self-destruct sometime very soon.