A bright blue background, a portrait of Mother Teresa printed on it, and a single sentence in huge letters: “I LEARNT A VALUABLE LESSON FROM THIS WOMAN, MOISTURISE EVERYDAY.”

To see where the joke comes from, it is enough to remember who Mother Teresa was. She took a vow of poverty, spent her life in the poorest neighbourhoods of Calcutta, won the Nobel Peace Prize and was declared a saint after her death. She is one of the first names the modern world thinks of when it thinks of self sacrifice.

Banksy takes this figure and places her directly into the visual language of a cosmetics advert, a bright flat background, a recognisable face, a slogan printed over it. In advertising this is called a celebrity endorsement, borrowing a face’s credibility for a brand’s product. The content of the sentence, meanwhile, is completely empty.

The critique works on two levels. The first is that even moral authority can turn into a marketable asset. The second is more insidious, the gap between admiring a figure and actually doing what she did. The narrator in the sentence says he learnt a valuable lesson from Mother Teresa, and that lesson turns out to be entirely superficial. All that is left of a whole life is a skincare tip.

The piece dates from 2006 and was shown at Banksy’s Barely Legal exhibition in Los Angeles, held between 15 and 17 September.

Banksy is not mocking Mother Teresa here. What he is mocking is the culture that can reduce even someone like her to an advertising face.