I believe most languages have a specific cadence and rules of order.For example the Chinese language in general uses "sound and pitch" to distinguish many words. Utter the wrong sound or use the wrong pitch and you may be saying the wrong word or indicating a different definition of the word. In the English language grammar is the rule. Without proper grammar the meaning and intention of your spoken word may be misunderstood or totally perverted.
It is necessary to precisely convey your thoughts.
Because not using it can change the context of what you are saying. For example;
"Let's eat, Grandma!" - This shows you are inviting Grandma to eat.
"Let's eat Grandma." - This shows Grandma is dinner.
The use of correct English grammar is important in order to avoid misunderstandings. If you make so many mistakes while writing or speaking English then this thing will slow down your communications. It is very hard to express the ideas and thoughts clearly if you are making so many language mistakes. Moreover nobody is going to tell you that you’re making mistakes. If you want to improve your grammatical mistakes, then I suggest you a best institute that help you to improve your communication skills. English-Pro provides best English Speaking Courses from basics level to high advanced level.
If you are to be taken seriously as an adult, especially within contexts where written material and communication is important, then correct grammar is essential.
I worked for a printing company a long time ago. One of the art directors left written instructions for a large printing job before going on holidays. His grammar and instructions were so poorly written that the text could be interpreted in three different ways. We could reach the client to ask. We couldn't reach the art director, so we guessed. We guessed wrong. The company ate an $80,000 error. The art director couldn't see what was wrong with his writing, but everyone else could. To prevent this from happening in the future, the guy was fired.