Looking at the naked woman depicted in a scene from Ruby, Bloom notes that the illustrator has preserved some decorum: "Sheet kindly lent." (And indeed it was in the actual printed book.) His phrase may irreverently echo the opening words of a popular hymn, "Lead, Kindly Light," the words for which were written by John Henry Newman (later Cardinal Newman) in 1833 as a poem titled The Pillar of Cloud. Molly thinks of this hymn in Penelope.
Newman wrote the poem as a young priest when his ship was becalmed for a week between Corsica and Sardinia, after weeks of illness in which he was desperate to leave Italy and return to England. The first stanza expresses his state of physical longing and spiritual faith, with one step completed and many more to go:
Lead, Kindly Light, amidst th'encircling gloom,
Lead Thou me on!
The night is dark, and I am far from home,
Lead Thou me on!
Keep Thou my feet; I do not ask to see
The distant scene; one step enough for me.
Set to several different tunes, the hymn has enjoyed great popularity. In the 20th century it was sung by trapped survivors of a mine explosion, by occupants of one of the Titanic's lifeboats, by troops going into the trenches in WWI, and by women being led to a concentration camp by S.S. troops.
Zack Bowen (Musical Allusions, 88) infers an allusion because of the verbal similarities between "Lead kindly light" and "Sheet kindly lent," and they are striking: assonance and near-alliteration (amounting to near-rhyme) in the first word, an identical second word, and identical alliteration at the beginning and the end of the third word. It is certain that Bloom knows the hymn, because Molly remembers how "he got me on to sing in the Stabat Mater by going around saying he was putting Lead Kindly Light to music I put him up to that till the jesuits found out he was a freemason thumping the piano lead Thou me on copied from some old opera." As a Catholic cardinal and a famous Catholic convert, Newman's authorship of the hymn would certainly have recommended it to Jesuits organizing a performance of sacred music.
What to make of Bloom's flippant reference to this inspirational religious song, in the context of a naked woman being beaten with a whip, is harder to imagine. He may simply be playing whimsically with the sounds of the words. But the effect is certainly at least a bit "witty"—a faculty he wonders whether he possesses.