The artist depicts the moment when Lancelot, having reached the chapel of the Holy Grail, falls into a deep sleep. An angel appears to him in a dream and announces that his quest will be in vain, as he is morally unworthy of finding the Grail because of his sinful relationship with Guinevere.
In this late-mature work, Burne-Jones condenses all the characteristic elements of his art: his interest in medieval subjects and mystical settings merges with a reflection on the destructive consequences of adultery and the fallibility of a heroic model of masculinity. The painter also revisits the stylistic influence of the early Renaissance, which was decisive for the early stages of his work.