It's simply the cornerstone. And upon it is all else is built in this free market system.

It is price.

You no doubt remember your college economics's professor drawing those two lines upon the board. The supply curve and the demand curve, and their intersection was the free market price.

And once discovered, price told you everything. Rising prices said that demand was good, and that producer's and suppliers were receiving increasing profits. While declining prices may indicate some trouble ahead.