An oratorio is a large musical composition including an orchestra, a choir, and soloists. The oratorio was somewhat modeled after the opera[dubious– discuss]. Their similarities include the use of a choir, soloists, an ensemble, various distinguishable characters, and arias. However, opera is musical theatre, while oratorio is strictly a concert piece—though oratorios are sometimes staged as operas, and operas are sometimes presented in concert form. In an oratorio there is generally little or no interaction between the characters, and no props or elaborate costumes. A particularly important difference is in the typical subject matter of the text. Opera tends to deal with history and mythology, including age-old devices of romance, deception, and murder, whereas the plot of an oratorio often deals with sacred topics, making it appropriate for performance in the church. Protestant composers took their stories from the Bible, while Catholic composers looked to the lives of saints. Oratorios became extremely popular in early 17th century Italy partly because of the success of the opera and the Church's prohibition of spectacles during Lent. Oratorios became the main choice of music during that period for opera audiences.
During the second half of the 17th century, there were trends toward the secularization of the religious oratorio. Evidence of this lies in its regular performance outside church halls in courts and public theaters. Whether religious or secular, the theme of an oratorio is meant to be weighty. It could include such topics as Creation, the life of Jesus, or the career of a classical hero or biblical prophet. Other changes eventually took place as well, possibly because most composers of oratorios were also popular composers of operas. They began to publish the librettos of their oratorios as they did for their operas. Strong emphasis was soon placed on arias while the use of the choir diminished. Female singers became regularly employed, and replaced the male narrator with the use of recitatives. Eventually, Monteverdi composed Il Combattimento di Tancredi e Clorinda which is considered to be the first secular oratorio.
The origins of the oratorio can be found in sacred dialogues in Italy. These were settings of Biblical, Latin texts and musically were quite similar to motets. There was a strong narrative, dramatic emphasis and there were conversational exchanges between characters in the work. G.Fanerio’s “teatro harmonico spirituale” is a set of 14 dialogues, the longest of which is 20 minutes long and covers the conversion of St. Paul and is for four soloists: Historicus (narrator), tenor; St. Paul, tenor; Voice from Heaven, bass; and ananias, tenor. There is also a four part chorus to represent any crowds in the drama. The music is often contrapuntal and madrigal-like. Philip Neri’s Congregazione dell'Oratorio featured the singing of spiritual laude. These became more and more popular and were eventually performed in specially built oratories (prayer halls) by professional musicians. Again, these were chiefly based on dramatic and narrative elements. Sacred opera provided another impetus for dialogues, and they greatly expanded in length (although never really beyond 60 minutes long). Cavalieri’s Rappresentatione di Anima e di Corpo is an example of one of these works, but technically it is not an oratorio because it features acting and dancing. It does, however contain music in the monodic style. The first oratorio to be called by that name is Pietro della Valle’s “Oratorio della Purificazione” , but due to its brevity (only 12mins long) and the fact that its other name was “dialogue”, we can see that there was much ambiguity in these names.
The most significant composer of oratorio latino is Giacomo Carissimi, whose Jephte is regarded as the first masterpiece of the genre. Like most other Latin oratorios of the period, it is in one section only.