Hello! I'm Venezuelan so I speak Spanish as my native language. A way to translate the passage is: What a wonderful occupation is to take the bus, get down in front of the ministry, break through the hits of envelopes with stamps, leave the last secretary behind, go inside steady and serious in the big mirrors office, exactly in the moment where a blue dressed usher gives the minister a letter. The thing is that the phrase you marked is a tricky sentence. You have to read it a lot of times to understand it. In the first moment that you read it you think that is is saying that he is rushing in between the envelopes with stamps and thats if you read separately " abrirse paso a golpes" but if you look closer he actually means that he is opening his way "abrirse paso" through hits of envelopes with stamps "golpes de sobres con sellos" .. the "a" is a connector that tricks you a little bit.