When the frequency of light matches the natural frequency of molecules in a material, light is absorbed by the material.
When ever a light falls on any object, the frequency of light should be more than, or at least equal to the frequency of light to be absorbed by the material, if the the frequency of light is less than the frequency of light, than the light will not be absorbed by the material, it will get transmit from the material.
Therefore if the frequency of light matches the natural frequency of molecules in a material, light is absorbed by the material.