The title means 'solemn'. The score says you can also use it as a sortie. It is quite majestic for a solemn piece!
For stops, it calls for ff on the great. The choir coupled to the swell provides the softer parts of the piece. It is split into two parts, the second part is played entirely on manuals, the first part uses pedal.
I registered it with Trombone 16' on the pedals, everything else up to Mixtures, and the Tromba on the Great. The octave couplers are on for each manual.
Louis Raffy (1868 - 1931)
Organist at léglise Saint-Nicolas de Nérac
The score can be found here:
http://javanese.imslp.info/files/imglnks/usimg/2/26/IMSLP132641-WIMA.dd1a-Raffy_Offertoire.pdf
Hope you enjoy! John