The truth is rarely pure and never simple.
The play by Oscar Wilde is deeply ironic and filled with his signature social humor. The two characters discuss the lie of one of them, who created a fictional relative to use his story for his own advances. When this character, Algy, tells about what he has done and laments that truth shall be pure and earnest, his companion replies with this quote. At first it can seem outright mind-blowing, because the fact that truth is indeed pure is one of the most popular cliches in any society. Still, when we read further and think about the context, we understand that the character (and the author) is right.
The society praises the truth but it is rarely ready to accept it fully, so the truth indeed can be grim and not at all simple to reveal. This statement is also interesting because it lets us understand some of the Wilde’s own struggling with the society and truth. As a homosexual man he had to constantly battle his nature, because in England of that time it was a serious crime. His homosexuality was the truth, but it would be most probably considered “not pure” by the society and it would be very difficult to spell this fact aloud and get along with it.