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The ashes of a red heifer burned entire (Numbers 19:5) when sprinkled on the unclean made them ceremonially clean (Heb. 9:13).
To cover the head with ashes was a token of self-abhorrence and humiliation (2 Samuel 13:19; Esther 4:3; Jeremiah 6:26, etc.).
To feed on ashes (Isaiah 44:20), means to seek that which will prove to be vain and unsatisfactory, and hence it denotes the unsatisfactory nature of idol-worship. (Compare Hos. 12:1).