This euphonium solo was written by William Himes, based on the song by Herbert H. Booth. The words of the chorus: "Christ is all, yes all in all. My Christ is all in all." The piano accompaniment was arranged by Gerry Shoults.
The following video features the composer William Himes performing this solo with The Salvation Army Oshawa band. Here is an interesting background story provided by Heather Allington about this composition: https://saoshawa.ca/my-christ-is-all-in-all/.