"The median sermon examined in the first survey was thirty-seven minutes long; Catholic homilies were the shortest, with a median of fourteen minutes."

"Not even that brevity satisfies Pope Francis, who recently advised clergy members to keep their sermons short: 'A homily, generally, should not go beyond ten minutes, because after eight minutes you lose people’s attention.'... By contrast, Pew found that the sermons at historically Black churches were the longest, at more than three times that length, with a median of fifty-four minutes. These sermons had only a few hundred more words than those from within the evangelical tradition, a detail that suggests oratorical style or musical interludes might be contributing to their length. The religion scholar Albert J. Raboteau wrote about this patient style of preaching, sometimes known as the 'black folk sermon' or 'old-time country preaching,' tracing its origins back to the eighteenth century in rural, Southern prayer meetings and revivals.... Vocabulary analysis by Pew revealed how common some language is across these four major Christian traditions—words like 'know' and 'God' appeared most often, not surprisingly—but also how distinctive certain words are within each of those traditions. Evangelicals referred most often to 'eternal Hell,' 'salvation,' 'sin,' 'Heaven,' and 'the Bible'; mainline Protestants relied more on the words 'poor,' 'house,' 'Gospel,' and 'disciple'; historically Black Protestants were most likely to hear 'hallelujah,' 'neighbor,' and 'praise.'... The appearance of certain words is hardly a sophisticated metric of anything, including sermons.... And even if Pew were able to parse the language of sermons in ways that shed more light on the views of preachers, it would not be able to illuminate the most fundamental question of preaching—when, whether, and why a sermon moves a congregant to new or deeper beliefs." 

From "What American Christians Hear at Church/Drawing on newly ubiquitous online services, Pew has tried to catalogue the subject matter of contemporary sermons," by Casey Cep (The New Yorker).