The following is an excerpt from "Van EycK" by J. Cyril M. Weale, published in 1912: 

In the centre-piece, "The Adoration of the Lamb," we discover the keynote to the scheme of the work, in the Apocalyptic Vision of St. John the source of its inspiration. The Lamb without spot, the blood from its breast pouring into a chalice, is stood on an altar, the white cloth over which bears on its superfrontal the text from the Vulgate, "Behold the Lamb of God, who taketh away the sins of the world," and on its stole-ends the legend, "Jesus, the Way, the Truth, and the Life." Worshipping angels gather around, some bearing instruments of the Passion, others swinging censers, their smoke laden with the prayers of the saints. In the foreground the Fountain of Life, flowing down through the ages along the gentle slope of flower-bejewelled sward, or dispensing its waters in vivifying jets from the gurgoyles beneath the feet and from the vases in the hands of the winged angel above its standard. To the four quarters groups of the elect: on the near right those of the Old Law and among the Gentiles who had lived in expectation of the Redeemer, the balancing group on the left typical of the New Law—prophets, doctors, philosophers, and princes in the former, the Apostles, popes, bishops, abbots, deacons, monks, and clerics among the latter. The corresponding groups back of the altar represent the army of martyrs whose blood is the seed of the Church, and the multitude of virgins. Over all, from the Holy Dove poised high over the altar, dart rays of light, emblematic of the Wisdom which had inspired their lives and of the fire of Love that had heartened their sacrifice. A carpet of flowers fills in all the open space fore of the altar, flowering shrubs and trees that of the mid-distance, while the entire background is an exquisite example of the realistic landscape-work that is an abiding charm of the Netherlandish school. The wonderful harmony of colour appeals at once to the senses; but more arresting, on nearer acquaintance, for its quality and felicity, is the wide range of portraiture that distinguishes the piece. From the two lateral panels in the dexter shutter the Knights of Christ and the Just Judges are pressing forward to the scene of the Vision, from the corresponding ones in the sinister shutter the Holy Hermits and the Holy Pilgrims: the former on spirited horses—an animal for which the painter evinces a special affection—the latter on foot. These panels are even more remarkable perhaps than the centre-piece for the diversity and multiplicity of the types portrayed, and for the wealth of landscape relieved by bird life lavished in their embellishment.

The "Adoration of the Lamb" is dominated in the upper zone by a triple panel, the centre framing the Almighty enthroned in majesty, whose is the kingdom, the power, and the glory—a supreme conception of the Eternal Father, unequalled for majestic stillness of face, intellectual power of brow, and depth and placidity of vision; on His right is the Mother of Christ, testifying to the full the lowliness of the handmaiden of the Lord, on His left St. John the Baptist, an earnest type, long of hair and rugged of beard, barefooted, and in a raiment of brown camel's hair girdled about the loins, intensifying the austerity of life ordained for him who was to prepare the way of the Lord and make straight His paths. In the "Choir of Angels," which is the subject of the first lateral panel in the dexter shutter, we have one of the choicest gems of the polyptych, and it affords us a measure of the distance the realistic tendencies of the painter had carried him from the traditions of the mystic school. Justified by the warrant of Scripture, he translates these spirit beings into purely human frames, but with a nerve system attuned to material sensations. In these angels there is no suggestion of trance-like ecstasy in contemplation of the Beatific Vision; they are angels materialised whose features reflect the strain of sustained effort and the underlying sense of pain which in man is inseparable from the sensing of intense joy. Evidently the master had fathomed the secrets of the human heart: the sense possibilities of the spirit world were without his ken, so he humanised his angels and evolved types understandable of the people, and at the same time one of the finest angel groups of all art. So inexpressibly realistic are his conceptions that to the poet-biographer Van Mander, at any rate, it was actually possible to discern "the different key in which the voice of each is pitched." But poets are privileged beings. Accompanying the Choir in their song of praise with organ, harp, and viol are the balancing group of angels in the corresponding compartment of the sinister shutter, types that, strangely enough, are in striking contrast to the former, their features moulded in placid contentment. The extreme panels of this zone are occupied by life-size presentations of our First Parents after the Fall, nude figures painted from the life, with absolute fidelity to nature and masterly conception of type: in a demi-lunette over the figure of Adam we see Cain and Abel making their offerings unto the Lord, and in that over Eve the slaying of Abel at the hands of his brother. There is a tradition extant that the altar-piece was originally furnished with a predella painted in distemper, a picture probably of Limbo or of Purgatory, but no trace of this remains.

The closed shutters display, filling in the full width of the middle zone, the scene of the Annunciation. The Ethyrean Sibyl and the Cumaean Sibyl occupy the demi-lunettes above the middle portion of the Virgin's chamber, the lunettes above the lateral divisions showing half-length figures of the Prophets Zacharias and Micheas. Of the four compartments of the lower zone the inner ones contain statues in grisaille of St. John the Baptist and St. John the Evangelist, the outer ones figures in the attitude of prayer, eminently life-like, of the donor, Jodoc Vyt, and his wife, Elizabeth Borluut. Jodoc was the second son of Sir Nicholas Vyt, Receiver of Flanders,—a wealthy citizen who owned the lordships of Pamele and Leedberghe, besides several mansions in Ghent, of which city he was burgomaster in 1433-34, after filling various minor municipal offices: by no means a handsome type, though manifestly a capable and kindly burgher, well-set, with a somewhat low forehead, small grey eyes, and a large mouth with broad under-lip; neither do the short-cropped hair and growing baldness or the three warts on upper-lip, nose, and forehead make for attractiveness. In respect of looks his wife is the better favoured, striking the beholder as an indulgent lady, with much of the homely dignity and serenity of the finer type of Flemish matron.

The Great Polyptych had not yet reached completion when, on the 18th of September 1426 Hubert van Eyck passed away after a painful illness. How much of the work remained to be accomplished none can tell with any hope of approach to certainty. A whole volume would not suffice for a critical examination of the mass of contending theories that for the best part of a century has been squandered in the endeavour to allocate to the two brothers their respective shares in the execution of the picture. Remember that it had already been some ten years in the making, and that, although it did not receive its final touches from the brush of John van Eyck until 1432, nearly six years after his brother's death, this period of John's life, as we shall presently discover, was too fully occupied in the service of Duke Philip of Burgundy to have allowed of his spending any considerable proportion of it in the task of completion. Remembering also that John's art had been closely modelled on that of his brother, that none better comprehended his ideals or was more intimately acquainted with the working out of his conceptions, mindful, moreover, of the deep veneration in which he held his master's genius, we must suppose that he realised the obligation of conscientiously adhering to the art and technique of the picture as he found it, any obtruding originality in violation of which would have amounted almost to sacrilege: all this further enhances the difficulty of differentiating between the work of the two painters. Indeed, if so minded, the reader is probably as well equipped as the writer to solve the puzzle.