Purchase of goods

I'm buying a commodity, why the value is not immediately recognized as expenses in the building?

If you buy the goods will not be charged because you spent money in exchange for the goods get the value of which will take effect the building, inventory and is therefore attributable to your cash (but just in the form of goods). The sale you get the sale price as revenue and the value of the goods sold are the opposite costs that are booked at the same time. I destroy the goods or scruffy them, then revenue is € 0 and the cost of the raw value of the goods