According to the Ball Blue Book of Canning & Freezing:
Scalding is a critical step in preparing vegetables for freezing and must be done carefully. (This is a "must" for all vegetables to be stored frozen for more than four weeks, except those used exlusively for their flavor such as green onions, hot peppers and herbs.) Scalding cleanses the surface of dirt and organisms, brightens the color, helps retain vitamins and reduces the action of enzymes which would otherwise destroy the fresh flavor after about four weeks. It also shrinks the product, making packing easier.
The recommended scalding time for fresh green peas is 2 minutes. Be sure to have your ice bath prepared for shocking them before starting the scalding to avoid overcooking them.
Once shocked, remove from the ice bath to avoid leaching nutrients, flavor, and color.