There is a mitzwah, whenever one makes dough, to take a portion of the dough and devote it to God. Were there a Beit HaMikdash at present, this dough would be given to the Kohanim, in our days we burn it till it is inedible so that no one else will benefit inappropriately from this Holy dough.
The Rabbis teach that Man's creation was HaShem separating Challah from the world. The earth and the water were mixed into a dough, and from that dough, Challah was taken, and into that Challah, HaShem blew a divine soul.
We are a portion of the world, set aside in Holiness by HaShem, since the time of its creation.