A fevered intensity in this portraval of Saint Sebastian marks it as a characteristic work by Tanzio, whose native village of Varallo in the mountains north of Milan was a major center of popular piety. The painter has shown Sebastian, who was persecuted as a Christian under Diocletian, being rescued by angels after the assault on him by the Emperor's archers. The thickset figure at the right who tenderly steadies Sebastian's body for the angel's ministrations may be Saint Irene, who nursed the martyr back to health.
The visual excitement of Tanzio's portrayal serves to convey Sebastian's state of emotional transport and transcendence of bodily pain. Contributing to the fervid drama is the extreme compression of the composition. Tanzio's large, solid forms are crowded by the frame, seeming to twist and strain to fit its confines. If the vivid illusionism and sharp contrasts of light and dark -- pulsating in the drapery across Sebastian's lap and in the spiky patterns of expressively tapering fingers -- reveal a study of Caravaggio's art, Tanzio's use of discordant colors is uniquely his own.
More information on this painting can be found in the Gallery publication Italian Paintings of the Seventeenth and Eighteenth Centuries, which is available as a free PDF https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/italian-paintings-17th-and-18th-centuries.pdf