War March of the Priests was commissioned by the King of Prussia to provide music for Athalie, Racine's religious drama. This particular arrangement is by William Thomas Best ('WT Best'), an English organist and composer most well-known for his editing and arranging of instrumental works for organ. I recorded this on the Hauptwerk sample set of St. Mary-le-Bow by Lavender Audio.
Score: https://www.sheetmusicplus.com/title/felix-mendelssohn-war-march-of-the-priests-sheet-music/18907721?aff_id=478282