The picture depicts a story: Christ asks his disciples: “Why are you awake?” The students are not visible in the picture; they are on the side of the viewer. That is why Christ addresses every viewer, each of us, with the same question.
The painting depicts the plot: Christ addresses the disciples with the question: “Why are you awake?” The disciples are not visible in the painting, they are on the side of the viewer of the painting. Therefore, Christ addresses each viewer, each of us, with the same question.