People often cringe when writers or others act like the "Grammar Police." However, this tells you much about the importance of grammar and the lasting impression words can make on others. Frankly, poor grammar makes a person look uneducated and many people like pointing this out. That may seem harsh, but intelligence and a high level of education have always been associated with proper grammar usage and word choice.
Two Reasons to Improve Your Grammar
Grammar facilities efficient communication. Without a shared set of rules, people will have a tough time understanding other people. For example, imagine the difficulty of interpreting a written passage when there is no agreement on which punctuation marks mean what. Imagine if the agreed upon use of punctuation marks or subject and verb agreement had not been established throughout the centuries. Theoretically, people could still interpret written information without these syntax rules, but it would be both complicated and time-consuming, thus making inter-personal interaction much more challenging.
Grammar is essential for people who want to make the right impression on others. On the most fundamental level, someone who makes grammatical mistakes will be seen as careless or worse, uneducated. This perception will come with a lowering of trust in their capabilities. Conversely, this suggests that someone with excellent command and understanding of grammar can use it to persuade others, which can be especially crucial for ones in the secular business world, authors who are writing literature (novels, poetry, research papers), and other examples of the mature and refined writings.