Fra Angelico and the prodigy Masaccio are considered the major artists of their time–the second quarter of the fifteenth century–but their contributions were entirely distinct from each other. Of the two, Masaccio’s impact is easier to identify: He more or less laid the foundations for High Renaissance painting. His fresco cycle in the Brancacci Chapel has been described as the “school of Florentine painting” by the formidable sixteenth-century art writer Giorgio Vasari, since everyone who was anyone learned from his example, including Fra Angelico himself. Masaccio was the first to apply to painting the principles of perspective (discovered by the architect Brunelleschi), as well as the first to imbue his figures with roundness through the use of light and shade. It was from Masaccio that Leonardo learned chiaroscuro, the way bodies are defined by light and shadows from a single source of illumination. And everyone learned from Masaccio’s compositions how to group figures together in a natural way. When Vasari divided the Renaissance into three periods, he named one after Masaccio.

No period in art is named after Fra Angelico, but his achievement is arguably more profound–albeit more elusive–than Masaccio’s. The difference between the two quattrocento masters is essentially the difference between two kinds of illusion. Masaccio discovered how convincingly to make a two-dimensional figure on a flat plane look like a three-dimensional object in real space. Fra Angelico discovered how convincingly to create the illusion of a living figure whose exterior features express an inner spiritual state–the look of love, a state of devotion or one of anguish.

Contrasting the two artists in his great work on aesthetics, Hegel praised Fra Angelico for his invention of what the philosopher called “interiority”–“the investigation of inner coordination, the indwelling meaning of facial expressions.” Fra Angelico’s work is infused, Hegel writes, “with the fervor of a religious love remote from the world, with a conventual purity of disposition, elevation, and sanctity of soul.” He was not called Fra Angelico for nothing. But who would expect an exhibition of works by so pure a spirit, so naïve a faith, so innocent a vision to be the hottest show of the season? No one would say that the remarkable exhibition of Fra Angelico at the Metropolitan Museum of Art (through January 29) is likely to be the school for contemporary New York artists. But it is the show to which artists tell me they keep going back.

It was in the depiction of interiority that Hegel believed painting had found its highest vocation, one that, moreover, distinguished the art of the Christian era from that of the classical era, whose defining medium was sculpture. A Greek statue of Aphrodite embodies the idea of erotic love but tells us nothing about what is going on inside her mind. What Hegel describes as “the spiritual depth of feeling, the bliss and grief of the heart” would not have been in the Greek repertory. It would simply have been taken for granted that mothers and their offspring are bonded through love. Christianity demanded that paintings of the Madonna visually depict this love. Thus Hegel contrasts those pictures with an Egyptian image of Isis holding her child, Horus, on her knees:

In a general way the subject here is the same as it is in Christian pictures of the Madonna: a divine mother with her child. But the difference in the treatment and portrayal of this subject is enormous. In this pose…there is nothing maternal in [Isis], no tenderness, no trait of that soul and feeling which is not entirely missing even in the stiffer Byzantine pictures of the Madonna. What has Raphael, or indeed any other of the great Italian masters not made of the Madonna and the Christ-child! What depth of feeling, what spiritual life, what inner wealth of profound emotion, what sublimity and charm…does not speak to us out of every line of these pictures!

Fra Angelico’s masterpiece is the complex of frescoes he produced between 1440 and 1445, in the common spaces and cells of the Dominican convent of San Marco in Florence. As far as I know, Hegel never traveled to Italy. His knowledge of Fra Angelico was in all likelihood based on engravings of some of the more famous San Marco frescoes–The Annunciation, say, or The Coronation of the Virgin. Yet he must have recognized through these works that however much the Renaissance based itself on classical models, a face like that of the Annunciate Virgin would have been unthinkable in classical representation. The Greek sculptors were well in advance of quattrocento painters in handling human anatomy. The latter excelled in showing through facial expression and body language how a figure like Mary would respond to the astonishing revelation that she would give birth to an incarnate god. She bends forward, holding her hands to her middle, as if protecting the life that is already within while her face shows her contemplating the meaning of her new role. The angel genuflects, acknowledging the difference in their stations. The drama of disclosure is enacted within a loggia, in the execution of which Fra Angelico demonstrates how much he has learned from Masaccio. The perspective is impeccable. The rational order of the architecture contrasts with the cosmic disruption of the historical order. A new era has begun.

Fra Angelico was at the height of his powers in the San Marco frescoes. Several of these wonders appear in beautiful reproductions on the upper level of the show at the Metropolitan. By contrast, many of the works on the lower level of the Lehman Wing are primarily of an art-historical interest. The paintings here merely reflect the gloriousness of Fra Angelico’s vision, which comes through even in the reproductions on the upper level. The lower level shows the present state of art-historical scholarship: Several works now attributed to him were once thought to be by different artists. We must take the word of the scholars that these are autographed, or mostly autographed works. Despite their attribution, however, they have very little of the exalted interiority of the San Marco frescoes that so inspired Hegel. The Lehman Wing thus has something of the structure of Plato’s allegory of the cave. How, then, did Fra Angelico become the artist whose work is a place of pilgrimage, the man whose name was given to him only after his death in 1455?

Fra Angelico was born Guido di Pietro; he became Fra Giovanni when he entered the Dominican order. In his early paintings, the Renaissance hardly appears to have begun. Paintings like the early Crucifixion–which shows a semicircle of Roman cavalrymen and foot soldiers standing at the base of the cross and looking coolly upward as if waiting for Christ to die, while four holy figures in front of the cross support the Virgin, who has fainted–is a powerfully condensed demonstration of Auden’s observation about how well the old masters understood the meaning of suffering. But it feels like a Gothic painting, giving no hint that the Renaissance is about to dawn. It is difficult to know how to respond to the Penitent Saint Jerome, in a panel from Princeton University, since Fra Angelico merely restored parts of it. The small, circular depictions of saints from the predella of an altarpiece said to date from 1417 are exciting only because we now know them to be the work of the young Fra Angelico.

On the other hand, it is difficult not to be touched by The Nativity, from the Minneapolis Institute of Art, or the tiny Virgin and Child With Four Angels, from the Detroit Institute of Art, whatever their art-historical significance may be. In The Nativity Mary and Joseph, as well as the ox and the mule, kneel in adoration of the luminous baby lying on a mat of golden rays. A quintet of angels has settled on the thatched roof, and the gold leaf of the sky conveys the sense of a new kind of dawn. It is a celebration of the divine and at the same time entirely human. In Virgin and Child Jesus looks like a fifth angel, and the Virgin’s star-spangled mantle looks like a piece of the night sky. Her face displays the dreamy expression one sees on new mothers everywhere. From the perspective of the stone bench she is seated on, and the way the side walls of the manger converge toward a vanishing point, one can tell that the Renaissance has arrived. Space is now naturalistic; these scenes of holiness take place in the same world we live in.

Upon entering the upper level of the Lehman Wing, one faces a greatly enlarged panel from an altarpiece that still remains to be identified. The original can be seen on the lower level, together with several other panels that belonged with it. The catalogue essay devoted to this altarpiece–which tells when it was painted, for what site it was painted, what the subject of the main panels might have been–is a serious piece of scholarly detective work. The panel that has been reproduced and enlarged for the upper level serves another purpose. It helps define precisely at what point Fra Angelico emerged as the master of his period. And it inadvertently provides a test for determining which works belong to the period that made his name. The test: Any work that would be at home in San Marco belongs to Fra Angelico’s prime. None of the paintings thus far discussed from the exhibition would pass that test, however engaging they may be. But this painting does pass the test. Any work that can stand up to the great Annunciation is Fra Angelico in his prime, if not at his peak.

The painting is called The Naming of Saint John the Baptist. An elderly man at the panel’s left is seated in a walled garden, writing with great concentration. He is Zacharias, father of John the Baptist. There are six lovely women, wearing opulent gowns picked out in gold. One of them is Saint Elizabeth, holding the child destined to be John the Baptist, in a very different kind of garment than the shaggy skin in which he is conventionally portrayed. The biblical story partly illustrated by this scene, which viewers in Fra Angelico’s time would have known, is that Zacharias has expressed doubts about his son’s role, revealed by an angel, and has been struck dumb. His speech is restored when he writes: “John is his name.” The little panel has the poetry of Botticelli’s Primavera–beautiful women, beautifully dressed, are gathered in the open air in a flowered landscape under a blue sky. The work is luminous, and we can see what a remarkable colorist Fra Angelico was, something Hegel could not have gleaned from the engravings. All the panels that allegedly belong with The Naming of Saint John the Baptist show the same almost translucent robes. There is something of the Middle Ages in the enclosed garden, carpeted with flowers. But the organization of space, especially in the wall’s perspective, implies the innovations of Masaccio and the spirit of the Renaissance. Two great periods in the history of art thus overlap in The Naming of Saint John the Baptist.

As, in fact, they do in much of Fra Angelico’s work. Consider, for instance, the left panel of his Last Judgment, which shows a number of the saved dancing to Paradise in the company of angels. It is a vision of life as fine as could have been imagined. Men, women and angels are dressed exquisitely, their hair done up in elegant coiffures, wearing garlands as well as the nimbuses they deserve as tiaras of sorts, tracing the figure of a courtly dance, tripping across a flower-strewn park, indifferent to the torments of the damned on the facing panel, as they move in rhythmic circles toward eternal bliss. At the top of the panel, figures board a flight of clouds and move into a new and unimaginable state expressed by an expanse of golden emptiness. The physical beauty of the dancers, human or angelic, may be metaphorical, but it is a compelling advertisement for the rewards that await the faithful, and as art it is the high point of this show. As for their expressions, they do not look happy. They look appropriately solemn, perhaps reflecting on the test they have passed in life below, and relieved to have earned the glory they share with the angels.