First, I simply have an instinctive aversion to public displays of devotion, for much the same reason I object to public displays of affection between members of a pair-bonded unit. This might just be an English thing, but it embarrasses me on the person's behalf. It betrays a lack of a certain kind of social modesty. One keeps that sort of thing private. It's a thing appropriate to moments of sincere discussion between intimates.
I think (though he was not my favourite Catholic writer) I remember Thomas Merton also making a similar comment in Seven Story Mountain, along the lines of "There is something nauseating about pious talk".
The other reason is that it tends to cheapen the devotional life. Talking about, thinking about and praying to God is so important that it should not be tossed about like the wrapping on a bag of take-away.
But mostly I posted Fr. Faber's quote because of the ongoing debate about the Traddie world over nice vs. holy. Trads are notoriously given to very public displays of devotion (and insisting that they be conducted in the right way!!) while holding the knife ever-ready for the quick one between the ribs of anyone who crosses them. This tendency is hardly limited to the Traditionalist movement in the Church, but it certainly seems to be more prevalent as a community trait there.
They are ever-ready too, with the quick and often pat rejoinder when faced with any criticism: "The hard truth is better than the sweet lie". This is usually followed by recitations of Our Lord's open displays of anger against the pharisees and money-changers. Passers-by, non-Catholics and children, however, are often witness to these kinds of exchanges and I think are justified in going away disappointed. See how they love each other?
Well, I'm not a spiritual writer and it's not for me to correct, particularly since the quick and irritable rejoinder are defining characteristics of my own interpersonal and devotional life. I am faced daily with the temptation to the quick and snarky response.
I posted Fr. Faber's comment because I was relieved somewhat to learn that this is not a modern problem, that others greater and holier than I have observed it and fought against it. It's comforting to have companions in temptation.
The question of real vs. false devotion is extremely pertinent, and is a big part of Fr. Faber's very pointed writing on the spiritual life. Of course real devotion produces real sanctity, but it is only too easy to fall into the trap of presuming one's self devoted, and therefore superior to the general run of humanity, or even the general run of Christians. It is a salutary warning, and one that is repeated many times by C. S. Lewis and nearly all other writers on the Christian life.
It is for this reason I have banned excessive God-talk in the commbox, and the reason it tends to irritate me so much. I have found that in many, if not most cases when a person engages in gratuitous God-talk, particularly in a public forum, the person is much more likely to be talking about himself. Or herself, since it seems mostly to be a female vice.
In fact, this was proven to me quite aptly recently when a person who had left a particularly flowery God-talk commbox post became abusive and extremely nasty when I deleted his comment and said why. From the excessively POD language and tone, I had guessed that this was someone who was greatly enamoured of his own holiness and was very interested in demonstrating it for the world to admire. The incontinent note I received as punishment for daring to call him on his bullshit proved my suspicion to have been justified.
Don't keep your light under a bushel, by any means, but I think it's good advice to try to keep our phylacteries as narrow and our tassels as short as possible, yes?