Eero Sipilä was an organist by training. His liking for Gregorian chant left its mark on his compositions in the form of stylistic borrowings or at least reflections. In one of his letters Sipilä mentioned as his main work the quartet that was to be the last thing he wrote. The name Lux aeterna is a reference to the section in the Gregorian mass, melodic motifs from which dominate the entire quartet. There is no trace of the modernistic tendencies of the works composed in the 1960s, but the pungent seconds harmonies characteristic of Sipilä are all there.