Why did oratorios develop historically?

Oratorios developed historically primarily because church authorities frowned on opera during Lent and Advent. This was a significant factor in the evolution of the oratorio, as these periods in the Christian liturgical calendar are associated with solemnity and reflection, where the more secular and theatrical nature of opera was deemed inappropriate. Consequently, composers sought to create a new genre that could provide religious content while adhering to the stricter guidelines of the church.

Oratorios typically feature similar musical elements to operas, such as arias and choral passages, but they are not staged with acting or elaborate sets, which aligns better with the church's desire for solemn worship during these special seasons. This development allowed for the continuation of musical expression in a liturgical environment, leading to the rich tradition of sacred music that we recognize in oratorios today.