Montag's reaction to the commercial on the subway is a turning point in his life in Fahrenheit 451.How does he react and why?

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.