The most important thing is to be able to condense your goal into a crystal clear sentence. What is your goal?
OK, now why do you want to achieve these things; what do you plan to do with them?
Because accounting field gives me oppurtunities to work at offices. I dont deny physical jobs, but accounting is going to settle me in only one seat. I work with numbers, documents, computers and businessmen. This major also offers a stardard working time, 8 hours a day, makes my mind up and adapt a professional working system.
OK Let's break this down:
1 Accounting gives me the opportunity to work in an office
Many professions work in offices, so this does not seem a very strong factor to me. You should start with the strongest factor. How about something like this:
As someone who has always been interested in mathematics, accountancy appeals to me as it would allow me to use my skills in a practical way, doing one of the most important jobs in a company.
2 physical jobs
This isn't relevant- concentrate purely on what you have to give and what you want to learn.
3 This major also offers a stardard working time, 8 hours a day
This actually sounds a bit negative, as if you are that committed. You shoudl write instead about the positive things- working in a team in an office, using many different skills, etc