Most bacteria grow fast at temperatures between 25-37 degrees Centigrade, and slow at temperatures below 7 degrees. So by lowering the temperature, you slow down bacterial growth, and hence you slow down spoiling. But it does not stop completely, so if you wait long enough you would still have your milk go sour, your bread mold, and your cheese go green. It just takes longer.
Refrigeration slows the growth of bacteria, molds, and other micro-organisms.
In addition, refrigeration slows other chemical reactions, for example enzyme reactions, that are associated with the spoilage of food. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.