Yahweh speaks of a person worshiping an idol as if that person were eating the burned ashes of the wood from which he made the idol. Just as eating ashes does not benefit a person, neither does worshiping an idol. (See: [[rc://en/ta/man/translate/figs-metaphor]])
The heart represents the inner person. Alternate translation: "he misleads himself because he is deceived" (See: [[rc://en/ta/man/translate/figs-metonymy]])