This is the fifth chorale prelude of Johannes Brahms' Op. 122. It treats the chorale: "O Gott, du frommer Gott" (known in English as "O God, Thou Faithful God").
Considering the many colours of the organ and the texture of the piece, I decided for a varied registration making use of oboe and trumpet reeds of the organ, which might be highly different to a registration, one might do on a "romantik" organ.