I believe this work to be one of the very greatest of 20th Century symphonic choral masterworks. In other words, it deserves to be mentioned in the same breath as William Walton's Belshazzar's Feast, Leos Janacek's Slavonic Mass, Dmitri Shostakovich's Babi Yar, Franz Schmidt's Book with Seven Seals, Edward Elgar's Dream of Gerontius, Gustav Mahler's Symphony No. 8, Schoenberg's Gurrelieder and so on.
Big (lasting about an hour), bold and full of hummable tunes that will stick in your mind for a long time. Also heartfelt, from a composer nearing the end of his life and attempting -- successfully, in my opinion -- to reflect his own existential hopes, doubts and fears through the most expressive medium possible, resulting in incredibly powerful music. It is a shame that Lloyd's music never attained "fashionable" status among critics and conductors (with a few notable exceptions), and thus was rarely heard in the concert hall. But thanks in particular to the work of two companies -- Lyrita of the UK and Albany Records of the USA -- most of Lloyd's orchestral output can be heard in excellent recorded performances, many conducted by the composer himself.
In many ways, this is Lloyd's "Symphony No. 13" -- no soloists, but full chorus throughout. Among his instrumental symphonies, No. 4 and No. 5 stand out for me, but the Symphonic Mass is the finest of all. Truly the crowning work of this man's life. Do not miss it.