Sibelius originally intended his Seventh Symphony to be in three movements, but in the end fashioned it into a single movement. It is cast in four distinct sections, however: a substantial opening Adagio is followed by a scherzo-like section, and then another, larger scherzo (which may have been spawned by the "Hellenic Rondo" idea that Sibelius had originally spoken of in regard to this work), and finally a recall of materials from the Adagio section. Initially entitled "Fantasia sinfonica," the work was subsequently restored to its status of symphony by the composer and would serve as his last foray in this genre.
The Seventh Symphony came as the climax of a lifetime's work for Sibelius. His ongoing search for new formal procedures that began with his Second Symphony reaches its acme in this sweeping, motivically concentrated and highly integrated work, containing elements of both sonata form and of rondo form. While many scholars have attempted to come up with different ways to classify the Seventh, it is a futile mental exercise to fit the work into traditional formal schemes, so complete is Sibelius' mastery of transition and control of simultaneous tempos.
The Adagio begins darkly, the strings rising from their bass range but soon reaching brighter terrain as motivic bits are assembled and the main thematic material begins to unfold. Soon a somewhat somber passage begins in the lower strings, building slowly and taking on an increasingly passionate manner, culminating in a powerfully epiphanic declaration, where strings soar and then trombones gloriously resound the symphony's main theme. The Adagio section ends in a relatively subdued and bright mood.
The scherzo-like section begins almost seamlessly, evolving subtly out of the Adagio's closing material. The tempo gradually quickens and the music works up a dark intensity, but the resulting mood is generally playful and light in the first half, but menacing in the latter portion, where churning strings incite the orchestra to a torrent that culminates in a recall of the Adagio's trombone theme, now given a more somber treatment. The ensuing section is playful and lighter, but also develops some tension in its middle portion. The scoring here is fairly light and the tempo markings, Allegro molto moderato/Poco a poco meno moderato, come across as leisurely, but not brisk or driven.
Early on, the final section features another statement of the trombone theme, which is now confident and overpowering in its sense of triumph. The music thereafter moves from an angelic, almost rapturous passage for mostly unaccompanied strings toward near-stasis, before finally building from quivering strings to a resounding, all-conquering conclusion. This symphony typically has a duration of between 20 and 25 minutes.