Before writing your oratorio, you need to find a suitable source text. Most oratorios use text from the Bible (this may include stories or prayers) or detail the lives of the saints.
Score the sacred text. This entails breaking up the text for various voices. The sacred lines can be sung by solo voices and choruses as well. Structure the oratorio by reserving some sections for arias and other sections for choral presentation. Writing scores for an oratorio is similar to scoring an opera. However, an oratorio is without action.
Write music for the recitative of the oratorio. The recitative is the spoken portion of the oratorio that connects the various sections. It often describes narrative action and is spoken using one note.
Write the score for the instrumentation. Oratorios include musical accompaniment. This may be in the form of one or two instruments or an entire orchestra.