In 1922 a Masonic lodge, Suomi Looši No. 1, was established by American-Finnish freemasons, and Sibelius immediately became a member. Music played an important part in Masonic occasions, and at first Sibelius would occasionally play the organ at such events.
Sibelius's Op. 113 is a collection of ritual pieces for the Freemasons, consisting in all of twelve pieces. The first eight were first performed in 1927 and the last movements were completed in 1946 – even if Sibelius went on to make small alterations when the Musique religieuse was printed in 1948.
The original set of pieces was later extended by the inclusion of Sibelius's hymn Suur' olet, Herra (You are mighty, O Lord), which was already present in the first edition. This hymn may be the best-known of all the movements, as it also exists in arrangements for mixed choir and for male-voice choir.
Sibelius said that the Finlandia Hymn was not intended for singing – but, because it had already spread all over the world and had been provided with many different texts, he gave his approval to the text by his fellow Freemason Wäinö Sola, and the hymn was included in the 1938 version of the Musique religieuse (Masonic Ritual Music).
In the other movements Sibelius set texts by such authors as Johann Wolfgang von Goethe, Viktor Rydberg, Samuli Sario and Pao Chao. Sibelius’s last original compositions were the eighth and ninth movements of the Musique religieuse: Veljesvirsi (Ode to Fraternity) and Ylistyshymni (Hymn), composed in 1946.
For Aino's sixtieth birthday in 1931 Sibelius composed "To my beloved Aino" for piano four hands, a work that remained within his family circle.