The picture depicts the Annunciation by the Archangel Gabriel to the Virgin Mary that she will bear the son of God (Luke 1:26-38). The inscription shows his words: "AVE GRÃ. PLENA" or "Hail, full of grace...". She modestly draws back and responds, "ECCE ANCILLA DÑI." or "Behold the handmaiden of the Lord". Her words are painted upside down for God above to see. The Seven gifts of the Holy Spirit descend to her on seven rays of light from the upper window to the left, with the dove symbolising the Holy Spirit following the same path. "This is the moment God's plan for salvation is set in motion. Through Christ's human incarnation the old era of the Law is transformed into a new era of Grace".
The architecture moves from older, round Romanesque forms above, to (slightly) pointed Gothic arches below, with the higher levels largely in darkness, and the floor level well-lit. The gloom of the Old Covenant is about to be succeeded by the light of the New Covenant. The flat timber roof is in poor repair, with planks out of place. The use of Romanesque architecture to identify Jewish rather than Christian settings is a regular feature of the paintings of van Eyck and his followers, and other paintings show both styles in the same building in a symbolic way.
The decoration of the Temple is naturally all derived from the Old Testament, but the subjects shown are those believed in the Middle Ages to prefigure the coming of Christ the Messiah. In the floor tiles David's slaying of Goliath (centre front), foretells Christ's triumph over the devil. Behind this, Samson pulls down the Temple of the Philistines, prefiguring both the Crucifixion and the Last Judgement, according to medieval authorities. To the left, Delilah is cutting Samson's hair (Betrayal of Christ), and behind he slays the Philistines (Christ's triumph over sin). The death of Absalom and possibly that of Abimelech are identified by some art historians, although only tiny sections are visible. Erwin Panofsky, who first developed much of this analysis, proposed a scheme for the significance of the astrological symbols in the round border tiles, and other versions have been suggested.
The rear wall has a single stained glass window, where Jehovah stands, above triple plain-glazed windows below, which perhaps suggest the Christian trinity. On either side of the single window are dim wall-paintings of the finding of Moses by Pharaoh's daughter (left, pre-figuring the Annunciation itself), and Moses receiving the Ten Commandments (right, paralleling the New Covenant Christ would bring). Below them are roundels with Isaac and Jacob, for which various symbolic functions have been proposed. The lilies are a traditional attribute of Mary, standing for purity. The empty stool may be an "empty throne", a symbol for Christ going back to early Byzantine art.
It has been suggested that Mary has been given the features of Isabella of Portugal, wife of Philip the Good, Duke of Burgundy, who may well have commissioned the painting from van Eyck, his (part-time) court painter.. Mary wears a robe in her usual blue, which is trimmed in ermine, reserved for royalty, which would suit this theory, although the Middle Ages placed great emphasis on Mary's royal descent in any case. As is usual, especially in the North, Mary's features are less attractive than those of Gabriel; being a sexless angel there was considered to be no possibility of his beauty causing inappropriate thoughts in the onlooker. Neither figure has a halo; these were being dispensed with in Early Netherlandish art in the interests of realism - eventually the Italians would follow. Mary's posture is ambiguous; it is not clear if she is standing, kneeling or sitting.
Another of van Eyck's themes, and that of other Early Netherlandish painters, is indicated by the large cope over a dalmatic worn by Gabriel. This would, in a human, mark him as a celebrant or attendant at a High Mass. Mary is facing a table with a book about the right size to be a Gospel Book or Missal upon it, and has her hands raised in a gesture known as the expansis manibus. This is certainly to convey the alarm and uncertainty with which she usually greets the surprising apparition of Gabriel and his news, but is also a gesture used by a priest at certain points of a Mass. The painting has been connected with the Golden Mass ("Missa Aurea"), a liturgical drama, or dramatised Mass, popular in the Netherlands at the time, which included a staging of the Annunciation as the Gospel reading. More generally, this is part of a common theme in Early Netherlandish art, where Mary, as intermediary between the faithful and God, is compared to, or seen as, a priest celebrating Mass. Her personal sacrifice of her son is compared to the ritual sacrifice enacted by the priest in the Mass. In a surviving extreme example in the Louvre she is shown clearly wearing vestments and celebrating mass at an altar; more often, as here, the comparison is made more subtly.
A cleaning in 1998, and examination by modern technical methods such as infrared reflectograms, has revealed much about van Eyck's technique here, which is consistent with other works of his such as the Arnolfini Portrait. His underdrawing has been revealed, and so have many changes made in the course of painting the work.
Van Eyck's superb oil painting technique is evident throughout. Gold leaf is only used for the seven rays coming in from the left; paint is used for all the gold on Gabriel, often worked wet-on-wet to achieve the textural effects of his brocaded clothes. In a shadowy area behind the stool van Eyck worked a glaze with his fingers. The play of light over the many different textures in the painting is brilliantly rendered, and the illusionistic detail, especially in Gabriel's rich costume, is exceptional.
Apart from several small changes in the position of hands and faces, the under-drawing shows that the small pilasters on the left wall were originally planned to be repeated on the rear wall, and to be much taller, reaching nearly to the roof, on both. The paint on the rear wall is thicker than on the left wall, so he may have painted the pilasters before changing his mind. In the underdrawing the ceiling planks are all in place, and there was also a light source to the right, for which the shadows are drawn.
The narrative scenes on the tiles replace a simpler decorative plan in the underdrawing, and the stool has become much larger. The vase of lilies was not only absent in the underdrawing, but was not reserved, that is to say that a space was not left for it in the paint for the Virgin's robe or the floor. This suggests it was only added late in the course of painting.
Examination of other major van Eyck works reveals similar developments from the underdrawing, and in the course of painting, in these works. It seems van Eyck, perhaps acting with clerical advisers, although he appears to have been a considerable reader himself, liked to add further complexity to his compositions in the course of work on them.
The range of dates given for the painting, was previously from 1428-29 (Panofsky and others) to 1436-37, but the discovery in 1959 of a date of 1437 on an altarpiece in the Gemäldegalerie Alte Meister, Dresden has considerably changed all van Eyck dating, and "makes it all but impossible to continue dating the Annunciation before 1432" (Hand). The painting appears stylistically to come between the Ghent Altarpiece and late works such as the Berlin Virgin in a church.
Two authorities have considered the painting to belong to Jan's brother Hubert van Eyck, who died in 1426. It is thought that the recent cleaning or technical investigation has tended to confirm the majority view that it is an autograph work by Jan.