A. Challah recalls the manna bread that sustained the Jews in the wilderness. The Friday double-portion of manna is why we have two loaves of challah on Sabbath. The Manna was covered with a thin layer of dew, which is one reason for the cover. Another reason is that bread is always the highest and most important of our blessings during a meal. It represents our basic staples and nourishment. But on the Sabbath we begin with the Kiddush blessing on a luxurious cup of wine – so as to not ‘shame’ the importance of simple and basic bread, we cover them while Kiddush is said.