More than one Eliot biography has cited the game that men of The City
liked to play. They would find an unusual passage from the world's
most perspicacious fictional detective and challenge the others
to identify the episode in which that passage was to be found.

The following seems complete outside the context in which it is to be found.
Given its content, it is hard to think that Eliot didn't use it for the
game, or have it used on him.

" 'What a lovely thing a rose is!'
He walked past the couch to the open window and held up the drooping stalk
of a moss-rose, looking down at the dainty blend of crimson and green. It
was a new phase of his character to me, for I had never before seen him show
any keen interest in natural objects.
'There is nothing in which deduction is so necessary as in religion,' said
he, leaning with his back against the shutters. 'It can be built up as an
exact science by the reasoner. Our highest assurance of the goodness of
Providence seems to me to rest in the flowers. All other things, our powers,
our desires, our food, are all really necessary for our existence in the
first instance. But this rose is an extra. Its smell and its colour are an
embellishment of life, not a condition of it. It is only goodness which
gives extras, and so I say again that we have much to hope from the
flowers.' "

A very careful examination of the context does more than justify this
passage's place in the story.
Like most such things in these stories, seeing that justification requires a
challenging degree of perspicacity.