Christ has just cut his palm on the nail left in the door they are making and a drop of blood has fallen on to his foot, prefiguring the Crucifixion. In the background the dove perched on the ladder is a symbol of the Holy Spirit and the carpenter's triangle of the Trinity. The future John the Baptist is shown bringing water to bathe the wound, but the water also refers to the baptism. It has been suggested that the whole scene symbolises the interior of a church, with the bench representing the altar and Christ and his mother on the holy, east side of it. The partition behind it would represent the rood screen dividing the sacred part of the church, the chancel. from the nave. The sheep would represent the congregation, Christ's flock.
The painting was viciously attacked by the critics, partly for its realism which defied all current expectations that religious art should depict the Holy Family in a highly idealised way. The elaborate symbolism also seems to have aroused strong feelings in relation to the violent controversy going on at precisely that time over the introduction of Roman Catholic style ceremony and furniture (e.g. rood screens) into the Church of England. The realism of the picture in particular appears to have upset Charles Dickens, who delivered an amazing, heavily sarcastic, denunciation of it in his magazine Household Words:
'You behold the interior of a carpenter's shop. In the foreground of that carpenter's shop is a hideous, wrynecked, blubbering, red-headed boy, in a bed-gown, who appears to have received a poke in the hand, from the stick of another boy with whom he has been playing in an adjacent gutter, and to be holding it up for the contemplation of a kneeling woman, so horrible in her ugliness. that (supposing it were possible for any human creature to exist for a moment with that dislocated throat) she would stand out from the rest of the company as a Monster, in the vilest cabaret in France, or the lowest ginshop in England ... Wherever it is possible to express ugliness of feature. limb or attitude, you have it expressed. Such men as the carpenters might be undressed in any hospital where dirty drunkards, in a high state of varicose veins, are received. Their very toes have walked out of Saint Giles's'.
Simon Wilson, Tate Gallery: An Illustrated Companion, Tate Gallery, London, revised edition 1991, p.82