If English is not your first language, it is almost certain that your writing will contain errors. This may make it difficult for others to understand easily and quickly what you have written. In turn, your readers may give up and put your writing aside.
Written communication presents a greater potential for problems in communication than does oral communication. You are not usually there to reword a phrase or re-explain a paragraph if the reader does not understand what you have written. Consequently, there is a greater risk that your reader will not completely understand your message. As a result, writing requires greater accuracy and fluency in the language than does oral communication. Although errors made while speaking are quickly forgotten after a conversation has ended, what has been written remains. This includes any errors. Consequently, the standard for writing is higher than for oral communication.
If English is not your first language, you face all the challenges in writing that a native English speaker must overcome. However, you do not have the fluency of a native English speaker. This means that your vocabulary may not be as extensive as that of a native English speaker. Further, you will know with less certainty which words and word forms to use in various situations. The native English writer can rely on his or her instinct or experience. You cannot. You must possess the knowledge.
The foregoing explains why non-native English speakers usually need some help with their English writing, regardless of the level of their oral linguistic skills. The text, which appears on many websites, further illustrates this. Listed below are four pages that contain extracts of text taken from such websites.