ORATORIO is the genre of Handel's Messiah: "Hallelujah" chorus. Handel's Messiah (HMV 56) was composed in 1714 by George Frideric Handel. It was composed from the scriptural text compiled by Charles Jennens from King James Bible.
Oratorio is a large piece of music composed for groups such as orchestras, choir and some times solo singers. Oratorio involves the use of instrumental ensemble, choir and soloists. Oratorio is usually based on a religious theme and Messiah (HMV 56) by George Frideric Handel is a typical example of Oratorio. Another example is Hayden: The creation, The Dream of Gerontius.