Challah Boards

When G-d took the people of Israel out of Egypt, they traveled through the desert
for forty years on their way to Israel. During this time they were entirely dependent
upon G-d. Their food was manna, a crystal-like substance that fell from the
heavens each day.The Torah tells us,

“...ויהי ביום הששי לקטו לחם משנה שני העמר לאחד”
“...And it came to pass, that on the sixth day they collected
bread, two omers for each person...” (Exodus 16:22)

The two loaves that we eat on the Sabbath are symbolic of the manna. The manna
was covered with dew, above and below, so we too cover the challah with a cloth
on top and a board below.