Answer
Dello Joio's first major composition was "Magnificat," a choral work premiered in 1940. This piece marked a significant milestone in his career, showcasing his early talent and establishing him as a promising composer. "Magnificat" is a setting of the biblical text from Luke 1:46-55, known for its expressive melodies and rich harmonies. Its success helped launch Dello Joio's career and paved the way for his subsequent compositions.