Lemon symbolizes the human heart, light and love. It is known to bring in feelings of healing and love in addition to calming and a sense of well-being. So, with this in mind, it seems only fitting that lemon would be the ideal agent to help with energetic and spiritual cleansing.
Sometimes it is considered a symbol of longevity, purification, love, and friendship, and other times it is seen to be symbolic of bitterness and disappointment.