No facet of our lives is bereft of Avodas Hashem. Even our basic needs can be steeped with Kedushoh {Holiness}. The Chinuch says a person's life depends on eating bread, so Hashem wants to infuse this mundane necessary activity with Kedusha. Therefore, He commanded us to separate a piece of the dough and give it to the Cohen. This not only helps in the world to come but also adds Brocha to the physical dough itself. It is brought down that the letters of Challah (Ches, Lamed, Hey) is an acronym for Chelek Li’Olom Haboh. Maybe not coincidentally it also is Chelek Li’Olom Hazeh.
Similarly, the Gemoroh says that food of Klall Yisroel has a special ingredient called "Shabbos". We all know that when cooking and baking food for Shabbos, if one has in mind that it is special for Shabbos and says Lekovod Shabbos Kodesh, the food has a special heavenly taste on Shabbos.
