You could pay with cows, but that would make cows money. A particularly inefficient form thereof.

Fiat is valuable because others will accept it in trade for things you want.

A debt, IOU, all of these things are credit. Credit works in a high trust environment, and is more efficient than money. A tribe less than Dunbar’s number doesn’t need money. Credit, in the form of reputation, is sufficient.

For strangers, money is essential because neither party knows the reputation of the other. Or maybe they have a bad reputation. With money, antagonistic parties can still trade and benefit from the trade. With credit, the trade would never take place. Money allows trade that might turn enemies into friends.

Money is not the root of all evil. The LOVE of money is, because it’s better to love your wife, your children, and God. Loving money gets in the way of that.