The speaker is talking to someone who complains about commuting: the crowded trains, the heat, the harsh lights that seem to wear on the mind. The speaker gently disagrees. To them, a packed carriage should be a gift for any poet, full of faces that hint at whole histories and the small, odd details of ordinary lives. Even the corners of the carriage seem to hold the chance of something new.
The tone is warm but a little teasing. The speaker sounds puzzled rather than angry, as if the other person is missing something obvious. The final couplet makes the point sharply: perhaps you only see "the busy train you want to leave." Seeing the train as something to escape means you never really look at it. The title fits this idea. A "second glance" is what the speaker asks for, and the poem's short, quick lines mimic the jolting rhythm of a journey while it argues for slowing down and paying attention.