A: We should all (not only Rabbis) bless G-d for the food we eat, but that’s not what makes it Kosher. What makes it Kosher is what’s in it, and what was used to make it. Kosher certification is necessary to ensure that all the detailed and complex Kosher laws are strictly followed. Today’s sophisticated food processes require close and strict supervision. Kosher law requires that supervisors be not only knowledgeable of the many laws, but observant of them as well.
