Possible meanings are 1) the wounds represent the problems the people have as a result of their sin. Alternate translation: "They act as though my people's problems are not serious, like small wounds" or 2) the wounds represent the people's sin. Alternate translation: "They acts as though my people's sins are not serious, like small wounds" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "lightly" represents treating the wounds as if they were not serious, as if they were not difficult. (See: [[rc://en/ta/man/translate/figs-metaphor]])