The Hospitality of Abraham
Tretiakov Gallery, Moscow
In Orthodox Christianity the most common way to express the Trinity in an image is by illustrating the three men's visit to Abraham and Sarah's tent in Genesis 18. Because Genesis 18:1 calls this a visit of "the Lord," Christian tradition takes the number of visitors to indicate that "the Lord" appeared to Abraham as the Trinity. For this reason the men are usually depicted as angels, as here.
But Rublev abandons the other parts of the iconography, leaving Abraham and Sara out of the picture, reducing the meal to just a bit of meat in the traditional footed bowl, and rendering their tent as a built structure in the dim background, tall and slender like the visitors.
Read more about images of Abraham and the Trinity.
Source: Wikimedia Commons