An oratorio is a large-scale piece of music for choir, orchestra and vocal soloists, which tells a story without staging or costumes. Most oratorios are based on stories from the Bible, a source that Handel's English audiences knew well.
Enthir is a Bosmer sorcerer and merchant found at the College of Winterhold, and has connections to the Thieves Guild in Skyrim.
The warehouse is located at the southern end of Riften's docks. Orini Dral is patrolling the warehouse, and will immediately spot you. Sarthis is in the basement and will come rushing upstairs to aid his bodyguard. Orini is a modest opponent, but Sarthis can prove a difficult opponent to defeat.