This depends on whether you want to advocate for or against the closing.
To say that the closing would be good, you should focus on financial savings and on the idea that post offices are outdated in the modern world. You could say something like "With the US government drowning in debt and the rise of email and UPS, it simply makes sense to close the post office in my town."
However, if you want to argue the other side, you should argue that post offices still serve many people who would be left behind by a closure. For example, you could say "Although many people have access to email and UPS, there are many older people and people in rural towns like mine who would be cut off from easy communications without the post office."
I agree with the answer above. If you want to narrow your focus you might want to make a list of the variables (factors) that are likely to emerge if a post office closes. Some of those variables might be impact on community members (in the case above, seniors and rural citizens), unemployment issues, costs (either from competition or simply rising costs of US mail) and the impact of technology on the volume of business that the post office does. Pick two variables that relate (such as seniors and unemployment) and write a fill in the blank sentence. What is the relationship between closing the post office and how that will influence ______________ and _____________. It will be a short jump to coming up with your thesis statement from there.
Of course we are not for the closing of the post office and there are a lot of seniors that live in this area. Actually that is mostly what live here and some do not drive and some can't fill out money orders because they can't read or write very well and the post master does this for them. This is a rural area and the only post office within 20 miles. I need to pitch this this idea because this is a paper I am writing and I am not sure how to go about doing this or write the thesis. This is all new to me. Thanks