An interesting discussion - I would like to add some more suggestions.
I think Hinson's book "Liszt: Selected Intermediate to Early Advanced Piano Solos" would be very useful. In it are seven chorales, Christmas Song S102, Ave Verum Corpus (from Mozart), and The Shepherds at the Manger S186:3. These could easily lead to the many other pieces written by Liszt that have a religious name and/or theme.
Grieg's Lyric Pieces include a couple of Elegies, as well as "Bells", "Gratitude", "At Thy Feet" and "Wedding Day at Troldhaugen."
MacDowell's Sea Pictures No.3 A.D. MDCXX is a tribute to the Pilgrims.
Schumann's Op 68 includes the Chorale "Rejoice O My Soul."
Mendelssohn's Op.72 is Six Christmas Pieces.
Some of Burgmullers Op.100 Etudes have titles such as: Sincerity, Innocence, Sorrow, etc that could easily be incorporated into a Christian theme.
Gurlitt Op.140 n12 is "In the Church"
Rebikov wrote a colection of very easy pieces called The Christmas Gifts.
Many well known carols and hymns were written by composers such as Haydn, Mendelssohn. CH Parry wrote many works that could be used. Any work titled Elegie could fit into a religious theme. In addition, several earlier composers were members of the 'church' - Scarlatti, Soler, Vivaldi for instance.
I think it would be possible to use Spirituals and some Folk/National music quite effectively, e.g. Samuel Taylor-Coleridge's 'Deep River' and 'Steal Away'
Regards,
Elizabeth
Thank you for your suggestions.

For those of you that are interested, here is the list of pieces in vols. 1 and 2 of Hinson’s collection mentioned above:
Entrance composed by Anonymous
Aria BWV 515, composed by Johann Sebastian Bach
Choral BWV 514, composed by Johann Sebastian Bach
Pastorale Op. 100, No. 3, composed by Johann Friedrich Burgmuller
Tender Flower Op. 100, No. 10, composed by Johann Friedrich Burgmuller
Arietta composed by Johann Heinrich Buttstedt
Prelude Op. 28, No. 20, C Minor, composed by Frederic Chopin
Melody Op. 176, No. 3, composed by Victor Alphonse Duvernoy
Old Christmas Carol composed by Cesar Franck
Prayer composed by Cesar Franck
Song composed by Cesar Franck, from the Creuse.
Dedication Op. 1, No. 1, composed by Enrique Granados
Lullaby composed by Edvard Grieg, from Valders.
Andantino Op. 205, No. 1, composed by Cornelius Gurlitt
Moderato Op. 205, No. 2, composed by Cornelius Gurlitt
Sarabande composed by George Frideric Handel
Prayer composed by Genari Karganov
Album Leaf Op. 7, composed by Theodor Furchtegott Kirchner
Tranquil and Expressive Op. 62, No. 8, composed by Theodor Furchtegott Kirchner
Moderato composed by Johann Philipp Kirnberger
Andante Sostenuto Op. 72, No. 2, composed by Felix Mendelssohn
Allegro K. 3, Bb Major, composed by Wolfgang Amadeus Mozart
Canzonet (Song) composed by Christian Gottlob Neefe
Air D Minor, composed by Henry Purcell
Andante Op. 2, No. 2, composed by Alexander Reinagle
Elegy Op. 183, composed by Carl Reinecke
Prelude Op. 183, composed by Carl Reinecke
Song Op. 183, composed by Carl Reinecke
Larghetto K. 34, composed by Domenico Scarlatti
Sonata K. 32, D Minor, composed by Domenico Scarlatti
Andante composed by Franz Schubert
Chorale Op. 68, No. 4, composed by Robert Schumann
A Famous Melody by Beethoven composed by Robert Schumann
Litttle Cradle Song Op. 124, No. 6, composed by Robert Schumann
Little Study Op. 124, No. 6, composed by Robert Schumann
Melody Op. 68, No. 1, composed by Robert Schumann
Norse Song Op. 68, No. 40, composed by Robert Schumann
In Church Op. 39, No. 24, composed by Peter Ilyich Tchaikovsky
Morning Prayer Op. 39, No. 1, composed by Peter Ilyich Tchaikovsky
Serious Feelings composed by Daniel Gottlob Turk
Andantino composed by Johann Georg Witthauer
Song of the Shepherd Boy composed by Samuel Arnold
Prelude BWV 943, C Major, composed by Johann Sebastian Bach
Prelude BWV 934, C Minor, composed by Johann Sebastian Bach
Theme from Variations on "God Save the King" WoO 78, composed by Ludwig van Beethoven
Harmony of the Angels Op. 100, No. 21, composed by Johann Friedrich Burgmuller
Ave Maria Op. 100, No. 19, composed by Johann Friedrich Burgmuller
Largo BI 109, composed by Frederic Chopin
Prelude Op. 28, No. 6, B Minor, composed by Frederic Chopin
Prelude Op. 28, No. 4, E Minor, composed by Frederic Chopin
Poco Allegretto composed by Cesar Franck
Maestoso composed by Cesar Franck
Prayer Op. 43, No. 2, composed by Reinhold Gliere
Elegy Op. 46, No. 29, composed by Alexander Goedicke
Prelude composed by Charles Gounod
Arietta Op. 12, No. 1, composed by Edvard Grieg
Romanze composed by Franz Joseph Haydn
Rondo composed by James Hook
Andantino composed by Aram Khachaturian
Evening Song composed by Aram Khachaturian
Intermezzo composed by Theodor Kirchner
Consolation No. 1 G. 172, No. 1, composed by Franz Liszt
Song without Words Op. 30, No. 3, composed by Felix Mendelssohn
Charakterstuck Op. 7, No. 6, composed by Felix Mendelssohn
Etude Op. 91, No. 10, G Minor, composed by Moritz Moszkowski
Idylle Op. 94, No. 3, composed by Moritz Moszkowski
A Tear composed by Modest Moussorgsky, from Pieces Diverses.
Larghetto F Major, composed by Wolfgang Amadeus Mozart
Menuet composed by Jean-Philippe Rameau
Reconciliation Op. 17, No. 20, composed by Max Reger
Andante D. 29, C Major, composed by Franz Schubert
Theme Op. 145, composed by Franz Schubert
From Foreign Lands and People Op. 15, No. 1, composed by Robert Schumann
Mignon Op. 68, No. 35, composed by Robert Schumann
Theme with Variations Op. 188, No. 2, composed by Robert Schumann
Best wishes,
Bernhard.