In terms of a chronology of Monteverdi's development, his 1640 publication of the collection Selva morale e spirituale is normally paired with his eighth book of madrigals, which was published two years before. Selva morale is a huge collection, containing works in the fully progressive monodic style, as well as many in a more traditional polyphonic idiom. It is, in all likelihood, a comprehensive, or complete, collection of his sacred music composed during his years in Venice, where he had been since 1620. Some have called it a "forest" of music. Near the end, two remarkable magnificats can be found, the first for double chorus and instruments, the second for four voices "in a cappella style." This was at a time when a cappella polyphony had been out of date for decades. The magnificat may have been composed a very long time before publication, or it may show that Monteverdi had a sustained personal interest in the more traditional idioms, despite the fashion he himself was championing.
As magnificats must be, the work is divided into 12 sections, alternating between the madrigal-esque polyphony of three- or four-voice choral sections and statements of plainchant melodies. Conceptually, it's interesting to note the unintentional irony that each of these distinct textures represents in its way a foundation of a major phase in European music. On the one hand plainchant, the foundation of European melody, and on the other the harmonic system itself. Monteverdi had such a considerable hand in establishing the latter that even bluegrass players today owe him a debt. But aside from such extramusical considerations, the alternation simply provides a pleasing textural antiphony. The intimate choral sections effectively evoke the sound world of Monteverdi's madrigals but evoke a more fully interiorized sensibility than before. They tend to have either a gentle forward flow, or a kind of pulsing, cradle-like rhythmic sway. The influence of the grandiose Baroque style is apparent in the huge sonorous openings to many of the numbers. But even these are more modest than Monteverdi can be when at his most pompous, as he often is in his late sacred music. Here the gigantisms quickly fade into milder, meeker tones. On the whole, the magnificat secondo seems full of breathy space, with an airy lucidity of sound, especially in the trios. At the ends of sections, the music usually fades away gracefully as if receding into the distance. The prettiest section is probably the "Suscepti Israel," the most sonorous, and the most magnificent, the "Gloria Patri."