Montag hears the dentifrice commercial on the subway as he is trying to read the Bible. This is a very confusing passage. In what way is the commercial in the background interfering with his reading?

Montag is reading the wisdom of the ages. He is trying to comprehend the nature of man and God while a vapid superficial commercial drones on in the background. The juxtaposition between the meaningful and the meaningless is highlighted here.