In Cosimo Rosselli’s Sermon on the Mount, executed for the Sistine Chapel, the lower half of the composition is filled with about 100 figures. The figural groupings imitate the undulating lines of the hills, creating dynamic shapes that keep the viewer’s eyes moving across the composition that includes at least three distinct points in time.
At the centre left, Christ stands (rather than sits, as in Matthew 5:1) on a small hill. His right hand is raised in a gesture of declamation, indicating that he is about to begin his sermon, asking for the attention of the crowd, and signifying the importance of his teaching. The crowds stand and sit closely to the left and in front of Christ. The use of both imagined ancient and contemporary clothing, as well as the incorporation of an Italian town on the left and a church at the top of the mountain, thus incorporate past and present in the work, and underscore that Christ’s authority and teaching span both time and location. The disciples sit just behind and to the right of Christ.
Slightly right of centre and in the background, Christ leads his disciples down from the mountain after the sermon is over (Matthew 8:1). Finally, in the right foreground, Rosselli continues to draw on Matthew 8 by showing Christ healing a leper (Matthew 8:2–4). The leper, whose skin is covered with sores, kneels before Christ, who is stretching out his hand to heal him. This scene of healing may refer to the main theme of the Sermon on the Mount of true righteousness, not the external righteousness of the scribes and Pharisees (as perhaps represented by the bearded man wearing a long purple robe standing behind the leper), but righteousness of the heart. Christ’s care for the leper in need flows out of his righteous character into his relationship towards other people, moving from teaching to practical ministry.