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This article from Chabad.org provides biblical, Talmudic and halachic reasons for the custom of covering the challah before and during the HaMotzi blessing. In practice, the Shabbat challah is covered from the beginning of the Kiddush (blessing over the wine) until immediately before (or after – customs vary) the blessing over the bread, in which the challot are uncovered and cut. This article is particularly helpful for those looking to understand more about the various customs surrounding Bircat HaMotzi. Rabbi Menachem Posner is a teacher, educator, staff writer at Chabad.org and contributor to several online Jewish newspapers.