Retable of the Virgin of Montserrat

The artwork, is a masterpiece by Bermejo, a leading exponent of the Hispano-Flemish school, is a creation close to Flanders both in its general conception and style. The format of the triptych composed of rectangular panels, with hinged sides, is typical of Early Netherlandish painting from its beginnings, as are the figures painted in grisaille on the outside of the doors, namely the Archangel Gabriel and the Virgin, which go to create, in a closed triptych, the monochrome scene of the Annunciation, from which the incarnation of Christ originates, depicted as a child inside and therefore a necessary premise for what will be seen once the doors are opened. The two figures, standing on a molded base with veins painted to imitate marble, are represented standing to follow the vertical shape of the doors: the gait of the archangel, coming from the left, is suggested by the movement of the right leg, which protruding the foot from under the clothes, while symmetrically Mary's left leg, depicted with her arms crossed on her chest as a sign of humility, is slightly bent to indicate the beginning of the genuflection; the remaining space in the foreground at the feet of the figures, beyond the base, is occupied by bare ground strewn with rocks.[12]

The Saint Michael in London, with the figure of the patron similar to that of the Acqui triptych

Inside, the central panel depicts the Virgin immersed in the landscape with the Child on her lap, who holds in one hand a thread to which a goldfinch is tied, a prefiguration of his Passion, towards which he turns his head with a strong twist of the body. Maria is seated on a carpenter's saw which identifies her as Our Lady of Montserrat (literally sawn / serrated mountain, due to the characteristic profile of the mountain, represented in heraldry[13][14] and in art[15] with a mountain surmounted or crossed by a saw, in allusion to the legend that would have it cut by angels with this tool to make room for the monastery). The Virgin is depicted as Queen, with the crown on her head and very rich regal robes: the mantle, dark blue with gold guilloche on the outside and damask green on the inside, closed on the chest with a cope clasp, covers the red tunic with the flaps of ermine, under which another tunic of dark velvet shows its flap embroidered with pearls and precious stones. The donor is kneeling at the feet of the Virgin, who closely resembles, but surpasses in quality in the greater spatial ease and vividness of the portrait, the homologous figure present in the St. Michael of Bermejo in the National Gallery of London.[16] The wealthy merchant from Acqui holds a prayer book in his hands open to the page of the Salve Regina and directs his gaze together with his prayers upwards towards the Virgin; he is dressed completely in black, over a white shirt that can be seen in the collar and in the cut of the sleeves, with a tall cap of the same color; two rings on his hands suggest his wealth. The lawn on which he rests his knees and on which the scroll with the painter's signature is placed in the foreground, represented in perspective like a folded letter, is strewn with the flowers of May, the Marian month, among which the poppy is recognisable, the wild sage, stock, eryngo and bindweed.[17]

The background is taken up by a deep bird's-eye view of the landscape sloping down towards the sea, with two Gothic-style religious buildings: on the right, near the group, a Franciscan convent: from the church portal, dominated by a cymatium with inside, in the tympanum, a statue of the Madonna with Child in her arms, a young friar looks out; behind him, inside, we can see a bush of roses, another flower sacred to the Virgin and her attribute. On the side façade, in addition to a street crucifix, there are two arches, one of the two accessible by a staircase, which symbolize the cloister of the convent and the contemplative life that takes place inside it, personified by an elderly friar reading a book leaning on the parapet.[18] On the left, high up on a cliff overlooking the sea, stands a church with a high bell tower which could represent the ancient cathedral of the Priamar of Savona, the commercial base city of the Della Chiesa family.[19] The marina, in the center of the background, illuminated by a beautiful sunset sky, shows a port in the distance and some cargo ships alluding to the client's mercantile activity.[20]

The two side panels, of inferior quality, are attributed to Rodrigo and Francesco de Osona, owners of a very active workshop in Valencia in those years. It is possible that the setting of the two lower scenes is the work of Bermejo, who in any case did not have a hand in it, while the two upper scenes, with some stylistic and above all perspective characteristics closer to Italy, are believed not to be of his creation[21] The panels are divided in two horizontally: in the lower area there are two saints, while the upper half is occupied by two scenes from the Life of the Virgin, namely her birth, on the left, a rich domestic interior scene, and the Presentation of Jesus to the Temple, on the right, which since the first publication of the work by Pellati has been compared to the Italian Renaissance due to its perspective structure;[22] on the checkered floor, in the foreground, there is an inscription that has never been deciphered, probably imaginary. In the lower half of the left door Saint Francis is represented receiving the stigmata surrounded by nature, with Brother Leo sleeping and a castle in a lake in the background; in the right door the saint, described by Pellati cautiously as a "warrior saint", was recognized as Saint Sebastian because of the arrows in his hand; however, it is more likely to be St. Julian the Hospitaller, as demonstrated by some attributes such as the pilgrim's dress, the sword and the book and the hunting scene in the background, linked to episodes of the saint's life:[23] the two lower areas of the side panels, thus, are occupied by the patron saints of Francesco Della Chiesa, the client, and his brother Giuliano.