Mitzvah Kotel Images
A small piece of dough is separated from the batch before baking. Originally the separated piece was given to the Kohen, a descendent of Aaron who served in the Temple in Jerusalem. In Messianic times we will reinstate that practice. Until then, we burn that piece before we eat the bread from which it was taken.
This reminds us that whatever we are given is not for our use alone. If we have wisdom, good health or money, we are to put them to a Divine purpose.
Though this mitzvah was originally given to the woman of the house, it is for every Jew.
Upon separating the piece, one says the blessing:
"Blessed are You, L‑rd our G‑d, King of the universe, who has sanctified us with His commandments and commanded us to separate challah."