How does opera differ from an oratorio?

While both opera and oratorio are extended works that set a narrative to music using recitative, aria, and choral pieces, they differ primarily in their presentation and purpose.12

• Staging and Action: An opera is a staged theatrical drama featuring scenery, costumes, and movement. In contrast, an oratorio is typically a concert piece performed without theatrical action or scenery.314
• Performance Venue: Operas are performed in theatres, whereas oratorios are often performed in concert halls or churches, though they are not intended for liturgical use.12
• Narrative Style: Oratorios frequently employ a testo (narrator) to relate events, usually in recitative style, to move the story forward.12
• Subject Matter: While both can be sacred or secular, oratorios are most commonly based on sacred or semisacred subjects, often drawing from scripture.12

Ultimately, opera is a complex, staged musico-dramatic entertainment, while the oratorio functions as a large-scale musical composition that relies on the music itself to convey the narrative.32