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.
After the quest was Alduin's Wall was finished Delphine and Esbern stayed in Sky Haven Temple for as long as I stayed there. When I talked to Delphine immediatly after the quest I was able to start the quest Rebuilding the Blades. After I left Sky Haven Temple and returned I found out that Delphine and Esbern had left. Delphine went back to the Sleeping Giant Inn and Esbern went back to his place in the Ratway.