In this scene, Montag is riding on a subway and trying to memorize a part of the Bible. Meanwhile, however, there is a loud advertisement blaring over the speakers promoting "Denham's Dentifrice" - Montag tries to block out the noise as he reads from the Bible in his lap: "Shut up, thought Montag. Consider the lilies of the field" (p. 78). He begins to try and fight out the commercial in his mind so he can memorize the passage, but it's too difficult, so he begins to argue out loud and others begin staring at him. There are some suggestions to call the guard, but then the train doors open at his stop, allowing him to rush off. "Consider the lilies of the field" is a reference to Jesus' Sermon on the Mount, informing his followers that possessions are not important.
At this point, Montag is really noticing how empty and shallow his culture has become and so he questions everything. He had an outburst on the subway because he can now see how difficult it is to avoid the bombardment of the media and how no one seems to care or notice - nobody can have thoughts of their own anymore. He tries to read, but it's just too difficult.
As was mentioned in the previous post, Montag loses his temper and runs out of the subway after failing to recall a Bible verse on the train. In this scene, Montag cannot concentrate long enough to remember Matthew 6:28 because of the annoying Denham's Dentifrice advertisement that is blaring through the speakers. Montag compares his ability to remember the Bible verse to a sieve trying to hold sand. At this point on the novel, Montag becomes totally overwhelmed with Bradbury's dystopian society. In Montag's society, consumer culture is present at all times and individuals cannot escape the constant flow of advertisements. Montag is simply attempting to remember a short Bible verse, yet cannot because of the blaring advertisements. Montag is completely disgusted and frustrated to the point that he screams aloud before running off of the train. His reaction to the Denham's Dentifrice advertisement depicts his frustration and angst.