The Hymn concertato is a genre of hymn

Hymn

A hymn is a type of song, usually religious, specifically written for the purpose of praise, adoration or prayer, and typically addressed to a deity or deities, or to a prominent figure or personification...

 arrangement

Arrangement

The American Federation of Musicians defines arranging as "the art of preparing and adapting an already written composition for presentation in other than its original form. An arrangement may include reharmonization, paraphrasing, and/or development of a composition, so that it fully represents...

 for choir

Choir

A choir, chorale or chorus is a musical ensemble of singers. Choral music, in turn, is the music written specifically for such an ensemble to perform.A body of singers who perform together as a group is called a choir or chorus...

 in which varied

Variation (music)

In music, variation is a formal technique where material is repeated in an altered form. The changes may involve harmony, melody, counterpoint, rhythm, timbre, orchestration or any combination of these.-Variation form:...

 treatments of stanzas are written out, all based on the familiar tune, and almost always ending with a verse for the congregation to join on. Organ

Organ (music)

The organ , is a keyboard instrument of one or more divisions, each played with its own keyboard operated either with the hands or with the feet. The organ is a relatively old musical instrument in the Western musical tradition, dating from the time of Ctesibius of Alexandria who is credited with...

 with brass instrument

Brass instrument

A brass instrument is a musical instrument whose sound is produced by sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player's lips...

s and/or tympani are the usual accompaniment

Accompaniment

In music, accompaniment is the art of playing along with an instrumental or vocal soloist or ensemble, often known as the lead, in a supporting manner...

.

The term seems to be American, although the form appears connected to similar works by Vaughan Williams and Holst

Gustav Holst

Gustav Theodore Holst was an English composer. He is most famous for his orchestral suite The Planets....

 as well as possibly to the concertato

Concertato

Concertato is a term in early Baroque music referring to either a genre or a style of music in which groups of instruments or voices share a melody, usually in alternation, and almost always over a basso continuo...

style motets of the 17th century German composers whose descendants settled in the midwest.

A compilation of examples: http://choralnet.org/resources/viewResource.phtml?id=2437&lang=en&category=1