THEOSISCyrill of Alexandria
If anyone happens to 'touch...,' it is stated, '...the sores, or the bones... of the deceased, or of the coffin,' such a person shall be rendered unclean. By 'ulcerated,' we refer to a heart that is not pure, as if it has been bruised by earthly lusts or sinful desires. The bone of a dead person symbolizes a remnant of defilement. The coffin serves as a reminder of the uncleanness that has already occurred. For Satan can inflict wounds upon the heart. We can be partially overwhelmed by fleshly desires, and though we may not fall into every sin, we often find ourselves surrounded by its remnants, much like when one strives to conquer anger or greed yet fails to entirely evade pride.
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This suggests that some individuals remain burdened by traces of impurity, which can be indicated by the presence of a dead man's bone. Furthermore, even by merely allowing into our minds the memory of passions that have been vanquished and pleasures that have been buried, we can sometimes greatly sin.