The transcendent feature of Palladio's church interiors is a light that penetrates every corner with its warmth – a light as unique and as Venetian as that created on canvas by his contemporaries Titian and Veronese. It is produced partly by the large number and size of windows, by the orientation of the plan toward the path of the sun and by the dominance of the church over surrounding buildings; but above all, it is the nature of the reflecting surface that endows it with a special cast of humanity, even of sensuality, and differentiates it from the austere effects of equally well-lit late Gothic interiors.
Whatever is not architecture in these churches is set apart in niches and panels; no sculpture or painted ornament invades the surfaces of walls, vaults or domes. Those surfaces, and most of the half columns, pilasters, and entablatures, except for the parts requiring detailed carving, are stucco over brick, and must perforce be painted. Palladio could control in this way the colour and quality as well as the quantity of light. The matt stucco surfaces reflect the light candidly, and unevenly enough to reveal the human touch, as brush-strokes do in a painting (...) Actually, Palladio's interiors were closer to the spirit of contemporary Venetian painting than if they had been decorated ; both architecture and painting created artificial theatres for the play of natural light.
(J. S. Ackerman, Palladio)