In the old days, when classical music was reserved for upper-crust audiences, a lot of music got one or two performances and then was put away in a library and forgotten. That’s why a group like Magnificat, Warren Stewart’s 17th-century music band, is so much fun to see. Often their performance of a piece is the only chance you’ll get to experience it live. This time around, they take on an obscure but lively serenata (like a mini-opera) composed by the once world-renowned Alessandro Scarlatti (1660-1725). In Venere, Amore, e Ragione (Venus, Cupid, and Reason), the love goddess chides her son for spending too much time around reasonable people, but Cupid shows her that the company he now keeps is much better. Given the high-polish performances Magnificat is known for, this show is worth leaving your palazzo to see.