If we remain at the heart of the image under consideration, we have the impression that, by staying in the motionlessness of its shell, the creature is preparing temporal explosions, not to say whirlwinds, of being.
Gaston Bachelard, The Poetics of Space
The Brera Madonna contains a visual vocabulary that explores death, resurrection, and rebirth. The coral beads have two purposes in this painting, functional and symbolic. Renaissance infants sometimes used coral beads for teething. In the visual vocabulary of the Renaissance painter, they were also a symbol of resurrection and rebirth. The mother and infant Christ, flanked by attendants, echo the traditional composition of mother and adult Christ found in Renaissance depictions of the pieta. Note the single coral pendant which Francesca places on the right side of the infant's chest, a reference to the sword wound that Christ received on the cross.
The thematic focus on rebirth applies not only to the infant Christ but to his mother Mary as well. Over time Christian iconography had incorporated the rich visual language of the ancient pantheons. For example, Piero della Francesca includes the shell motif at the top of the Montefeltro altarpiece, providing a direct link to the earlier mythic tradition of the divine feminine. According to Roman mythology, Venus is the goddess of love, fertility and beauty. The castration of her father Uranus by her brother Cronus fertilized the ocean and from the fertile waters Venus arose. Artistic interpretations do not typically depict the actual birth but the moment when Venus arrives at the shores of Paphos (Cyprus) in a shell.
Art historians interpret Francesca's incorporation of the shell as a way of portraying the rebirth of the earlier Greco-Roman goddess in a new and sacred Christian form. The canopy above Mary provides a spatial link to Venus and her mythological arrival in a shell at Cyprus. Francesca has suspended an egg from the canopy, creating a mirror motif to the traditional pearl within a shell. The earlier nature-based goddess had as the fruit of her creative act the pearl. The reimagined Renaissance goddess has the egg, or "fruit of her womb," as a symbol of the incarnate word.