Pretty much the pick of this week's concerts is the San Francisco Choral Society's full-scale production of Mendelssohn's oratorio, Elijah. 300 singers, the California Chamber Symphony, and a roster of respected Bay Area soloists (Brian Thorsett, Wendy Hillhouse, and Rod Gilfry in the title role) will make this performance look and sound like the ones that inspired Mendelssohn. If you don't know this work, take the opportunity to hear why it's one of the very few 19th-century oratorio's that survive in the modern repertory.