the conversion of st.paul by caravaggio
The painting records the moment when Saul of Tarsus, on his way to Damascus to annihilate the Christian community there, is struck blind by a brilliant light and hears the voice of Christ saying, “Saul, Saul, why persecutest thou me. And they that were with me saw indeed the light, and were afraid, but they heard not the voice. ” (Acts 22:6-11). Elsewhere Paul claims to have seen Christ during a vision, and it is on this basis that he grounds his claim be recognised as an Apostle: “Have I not seen Jesus Christ our Lord?” (I Corinthians 9:1).
Caravaggio biographer Helen Langdon describes the style of Conversion as “an odd blend of Raphael and clumsy rustic realism,” but notes how the composition, with its jagged shapes and irrational light which licks out details for their dramatic impact, creates “a sense of crisis and dislocation [in which] Christ disrupts the mundane world.”
The principal actor lies in a dramatic pose in the foreground of the picture (he actually intrudes into the viewer’s space), with his arms outstretched in shock. He has just seen a vision of Christ and has been blinded by a celestial light. The divine nature of his experience is evidenced by Saint Paul’s closed eyes, stiff arms and his continued illumination from heaven.
Curiously, neither the groom nor horse seem to notice Paul’s spiritual awakening. The main contribution of the skewbald horse, which occupies more of the picture than anything else, is to contribute a sense of tension with its upturned hoof poised in mid-air as if about to strike the newly converted Paul, while the groom concentrates on holding the reins to prevent the horse trampling him.
X-ray examination revealed another, almost complete version of the scene under the present painting, in which the saint is shown fallen to the ground, on the right of the canvas, his eyes open, his forehead lined, and his right hand raised. 
The two lateral paintings of the Cerasi Chapel were commissioned in September 1600 by Monsignor Tiberio Cerasi, Treasurer-General to Pope Clement VIII who purchased the chapel from the Augustinian friars on 8 July 1600 and entrusted Carlo Maderno to rebuild the small edifice in Baroque style.  The contract for the altarpiece with Carracci has not been preserved but it is generally assumed that the document had been signed somewhat earlier, and Caravaggio had to take into consideration the other artist’s work and the overall iconographic programme of the chapel. 
However, Baglione does write that Caravaggio painted the first set in a manner different from his usual style. The intricately packed composition, which by itself seems so contradictory, is remarkably similar to the tangled left side of the final version of The Martyrdom of Saint Matthew (colorplate 16), which should have immediately preceded it chronologically. The source of light from the right, as in the final version, would be exceptional in Caravaggio’s oeuvre, but correct for the painting if it were installed on the right wall of the chapel. The support, the cypress-wood panel required in the contract, is only slightly smaller than the canvas now in place. The old bearded soldier, Christ, and the boy angel are familiar Caravaggio models, and the landscape is similar to that in The Sacrifice of Isaac. Finally, whatever questions have been raised about this picture, the brilliant/attura is undeniably worthy of Caravaggio himself; virtuoso details such as the helmet or the old soldier’s sleeve require a hand as skilled as his.
Only Baglione mentions that Caravaggio carried out two sets of paintings for the Cerasi Chapel. He wrote that the first pair was rejected because the donor, Monsignor Cerasi, did not like them (therefore they must have been completed before Cerasi’s death in May, 1601). Baglione had good reason to hate Caravaggio, so his statement may be suspect, particularly when unconfirmed by any other source as close to the scene as he was. Mancini was that close, and his only relevant comment is that Cardinal Sannesio owned pictures that were “copied and retouched” from those now in the chapel, a description surely not applicable to this painting. It is not specifically documented until 1701, when it was in Genoa bequeathed by Francesco Maria Balbi, from whose heirs it eventually passed to Prince Odescalchi. Many Caravaggio specialists have not felt able to place so crowded and confused a composition anywhere in Caravaggio’s oeuvre.
Also, Saul’s fellow soldier, an older but still well-muscled man, rises to his defense. In one hand he clutches a spear and in the other he raises his shield. Interestingly, this soldier doesn’t quite understand what he’s defending Saul against, for though Saul’s companions did see the light, they didn’t hear the voice of God that accompanied it.
Caravaggio visits the theme of St. Paul’s conversion on the way to Damascus at least twice. The one most people are familiar with is the one that’s dominated almost entirely by the stricken saint’s horse. That one is in the Cerasi Chapel of the Church of Santa Maria del Popolo. The other one, which is really called The Conversion of Saint Paul, is now part of the Odescalchi Balbi Collection in Rome.