Andrea Mantegna, Adoration of the Shepherds, c1450
Andrea Mantegna (c1431-1506) was one of the great painters of the Italian Renaissance, and this painting in particular expresses the ideas of its time. Adoration of the Shepherds is an exploration of the dissonance and harmony among different aspects of human experience. Mantegna depicts the natural world, the material world, and the spiritual world, and manages to unite these elements visually to represent their harmony under Christ. Each realm has its own section of the canvas: Mary and Jesus represent the divine, Joseph and the barn to the left represent the material, while on the right the natural world is presented by the landscape in the background and the two shepherds who come to worship Christ. In this painting, Mantegna also imports aspects of the Northern Renaissance (particularly the background landscape) into his Italian style, and I also find his use of color quite striking.
Note: This description is a paraphrased excerpt from a paper I wrote a few years ago about this painting. If anyone is interested in a more detailed analysis, just send me a message through the blog's contact form to the right.