Montag says this in talking to Clarisse. He is talking about the kerosene that seems to stay on him as a fireman in their culture. This is important because it shows how entrenched he is in his job. In fact, if he were to try to not go to work, for example, his job would come and find him. The government of this society ensures that this is his job. Furthermore, as Montag starts to think about it, he can't really remember how he became a fireman, he just did like his dad and father before him. He can never let go of the fact that he is a fireman, it is a part of his life. If he catches someone with a book, he is bound to call it in.
We see this become even clearer when he commits an act with his hand against the government. He can't seem to shake the evil he commits against the government. This seems to be a society in which there is no forgiveness or change, it is only that things are as they are.