The Last Supper, one of Leonard da Vinci's more famous artworks, is important for various reasons.
First, because the disciples are all displaying very human, identifiable emotions. "The Last Supper" had certainly been painted before. Leonardo's version, though, was the first to depict real people acting like real people.
Secondly, and of major importance - the technical perspective in Last Supper is incredible. You can see that every single element of the painting directs one's attention straight to the midpoint of the composition, Christ's head. It's arguably the greatest example of one point perspective ever created.
The Last Supper is Leonardo's visual interpretation of an event chronicled in all four of the Gospels (books in the Christian New Testament). The evening before Christ was betrayed by one of his disciples, he gathered them together to eat, tell them he knew what was coming and wash their feet (a gesture symbolizing that all were equal under the eyes of the Lord). As they ate and drank together, Christ gave the disciples explicit instructions on how to eat and drink in the future, in remembrance of him. It was the first celebration of the Eucharist, a ritual still performed.
Specifically, Last Supper depicts the next few seconds in this story after Christ dropped the bombshell that one disciple would betray him before sunrise, and all twelve have reacted to the news with different degrees of horror, anger and shock.
His artwork comprises of a mixture of various techniques, which include the innovative techniques that he used in laying on the paint, his detailed knowledge of anatomy, light, botany and geology, his interest in physiognomy and the way in which humans register emotion in expression and gesture, his innovative use of the human form in figurative composition and his use of the subtle gradation of tone.