Writing is a skill and, like other skills, has to be learnt. In fact, writing is a lot more than just using accurate grammar and choosing appropriate vocabulary. Writing accurately is, of course, important, but there are a lot of other aspects to consider.
Every language has special phrases which can be used for a particular purpose.
For example, if you are writing a letter in English, it is usual to start by referring to a previous letter or meeting. If you wish to offer the reader further assistance, there are special phrases you can use at the end of your letter. You may wish to make a recommendation. Again, you will need a special phrase. These functional phrases are very important because they act as signals to the reader - they make your messages clearer to the reader.