"Approach with caution!" That warning should have been posted at the entrance to the pair of galleries featuring "Rembrandt's Late Religious Portraits" at the National Gallery of Art. The exhibition of 17 oils from the late 1650s and early 1660s, organized by NGA curator Arthur K. Wheelock, are deeply affecting, even upsetting in the depth of their feeling.

The figures -- saints, evangelists, Christ, the Sorrowful Virgin, possibly a monk -- are containers for personal dramas, dark in tonality. Struggles of faith test the subjects of these works and Rembrandt in turn tests us by so profoundly expressing their sobering thoughts, worries, sorrows and conflicting emotions.

The half-length figures are quiet, but their faces display immense mental and emotional energy. Lined brows, putty-like hands and drooping eyelids show exactly the physical cost of their inner turbulence.

Each figure is rapt, obsessed and intense, like Rembrandt's Bearded Man in a Cap from 165(7?). The painting is in the show because the figure may actually be a Jewish rabbi -- and it contains something elusive. (If this face looks familiar, it may be because the same model appears in at least four other works, including Rembrandt's Aristotle Contemplating the Bust of Homer at the Metropolitan Museum.)

Rembrandt's approach to particular works varies. This is important, as there has been speculation by several scholars that the late religious portraits were part of a series. Peter Paul Rubens and Anthony van Dyck, among others, had executed such series of apostles and/or saints, sometimes including Christ and the Virgin.

Perhaps Rembrandt did think of them as a group; but his series is irregular. It contains more than one interpretation of some apostles and none of others.

Rembrandt's financial reverses and emotional upheaval during this period certainly could have triggered such a series, concentrating on images of ordinary people probing for faith and emotional sustenance. But none of these works were known commissions and, in fact, during this period the artist enjoyed far fewer commissions than in the past.

Rembrandt (1606-1669) was wildly popular in the 1630s and early 1640s, but was considered somewhat passé by the 1650s. Dutch paintings were becoming more refined and more idealized, but Rembrandt's were earthy and broadly painted. Just take a look at The Apostle Bartholomew from 1657. His brow is so furrowed, one would think that the knife he holds, the eventual means of his martyrdom and his traditional attribute, had already been used on his forehead.

In 1661, Rembrandt paints another The Apostle Bartholomew. This figure is older and even more broadly modeled. The knife is less menacing, almost an accepted after-thought and less haunting than the face -- decrepit, resigned and still thinking -- that peers straight out at the viewer.

Rembrandt's wife Saskia had died in 1642, and his mounting financial losses ended in bankruptcy in 1656 and the sale of his huge art collection and home in 1657-8. He was taken to court by one woman who accused him of breaking a promise to marry her and Rembrandt eventually had a child with another, Hendrickji Stoffels, who was looked down upon for her out-of-wedlock birth. By 1659, Rembrandt was living with her and his only surviving child, Titus, in a new, smaller house.

Rembrandt's last portrait of his companion is Hendrickji Stoffels (as the Sorrowing Virgin?) from 1660. She would die, probably of the plague, in 1663. Titus would die at age 26 in 1669, about six months before his father, leaving behind a daughter.

Several of Rembrandt's late religious portraits are linked in style and with a black painted border; others may have been part of yet some other mini-series. The show can't answer all the questions these paintings raise, but the opportunity to view these moving works together is not to be missed.

Perhaps the most interesting series is not one that Rembrandt organized as such. Three canvases are devoted to Saint Paul. Two were painted from models and one is a self-portrait. Saint Paul, according to the show's excellent catalogue, was more important than Saint Peter for protestants and was a humble man who emphasized grace over law.

Though we know little of Rembrandt's personal ideas on religion, he based many of his works on scripture, from his first dated painting to have come down to us, his Stoning of Saint Stephen from 1625 in which he gave a spectator his own features, through self-portraits in the guise of Biblical (and other historic) figures in his portraits historiés.

One of the two portraits using a model, An Elderly Man as the Apostle Paul, from 165(9?), is probably the most intricately worked and lovingly detailed painting in the exhibition. Each hair and wrinkle is precisely defined in this thinker humbly lost in his own musings. The other portrait, the more broadly worked The Apostle Paul, dates from around 1657. The figure sits at his desk, worrying his epistle into being.

Rembrandt's Self-Portrait as the Apostle Paul from 1661 is one of the great pictures in western art and one of the most complex. The heavily impastoed and harshly lit face turns his slightly unkempt and elderly features toward the viewer, presenting his work to the viewer as if he cannot believe he has written it, as if it were all a dream. His sword, the attribute of his martyrdom, is barely visible and sticks out from his doublet. The way Rembrandt painted the sword, it looks like the hilt is already buried in his body.

After its debut at the National Gallery of Art, "Rembrandt's Late Religious Portraits" appears at the J. Paul Getty Museum in Los Angeles, June 7-Aug. 28, 2005.