Rautavaara's output has gone through several stylistic periods: neoclassicism (up to 1957), a first serial period (1957-65), neo-romanticism (1967-83), a synthetic second serial period (1984-94), and a “mystical” style (since 1994). These periods witnessed no change in the composer's aesthetic but rather broadened it. Rautavaara has described how modernism (or structuralism), mysticism, and Finnish-nationalism have been particularly important for his music and have found expression throughout his career. Mysticism in particular has shaped his development for a long while, with his most recent “mystical” style representing the culmination. Rautavaara claims that he has been fascinated by metaphysical and religious subjects as well as texts from childhood, and that this fascination has influenced his music and aesthetics. Although he grew up in the Lutheran tradition and faith, he does not belong to any religion and church: “My background was Lutheran, but I never really worried about different ‘creeds.’ I fear that my ecumenical relationship to the various churches meant indifference to their dogmas and theology.” This unrestricted attitude allowed Rautavaara to compose works to texts from the Orthodox liturgy, the Roman Catholic Church, and the shamanistic Kalevala. Some of his instrumental compositions also received titles that point to religious sources, such as Icons for piano (1955), Ta Tou Theou for organ (1967), and Laudatio Trinitatis for organ (1969). Thus Rautavaara regards himself as an “ecumenical” composer, that is to say, one who believes in religiousness as a feeling for and affinity with infinity. He sometimes uses sources from various religions simultaneously, such as in his opera Thomas,73 or gives his compositions titles that point at religious topics, characters, or symbols without reference to a particular religion, as in the Piano Sonata No. 1 Christus und die Fischer (1969), the Organ Concerto Annunciations (1976-77), the String Quintet Les Cieux Inconnues (1997), and the series of compositions referring to angels that is the subject of this study. He can be considered a mystical composer not because of such references to religious texts, subjects, and symbols, but rather because of his philosophy about music and his perception of the artist's role.

The term “mysticism” is used in various religions to express feelings beyond human experience: something that is the result of an inexpressible experience of contact with an ultimate reality, God, divinity, or spiritual truth.