I am basing all of the information I am about to put forth without any past knowledge of the Bible and whatever this painting means.
In the center of the painting is the main character of the piece, Saint Matthew. This is very odd for a Caravaggio painting because mainly his main characters are seen being off-center as compared to the rest of the painting and the surrounding inside of the painting. Saint Matthew has become a martyr at this point in his evangelistic career. He is adorned with a white bandana and a loincloth. Everyone around him are possibly Romans who do not believe in Christ and are wishing to destroy him and anyone who is spreading the belief of him across the world, as Saint Matthew was at the time. The man atop the cloud in the upper right-hand corner I believe is an angel who is reaching down from the clouds with a bow who is trying to assist in Saint Matthew's fight against the Romans as he nearly escapes their persecution. This painting is very brownish while showing a horrid scene from the Biblical past.
