Well, I hate to be the bearer of bad news, but all languages have a grammar component, even your native language. You just don’t realize you’re using it once you leave school and don’t study it formally anymore.
Grammar (or structure) is essential for communication; it is like a code used by the speakers of a language that allows people to express their ideas precisely, in a way that is easily understood by all who use that same code. When you accidentally change that code (when you make a grammar mistake), your message is likely to be misunderstood, or you may convey a different meaning than what you had intended.
In a nutshell, grammar allows you to be direct, or soft, or authoritative, or inquisitive, or polite, or assertive, or rude, whatever you want to be when expressing your ideas. Let’s take the example of something that happened this week in aviation.
Last Monday, there were moments of fear for the passengers of a Boeing 737 when they felt the aircraft drop several thousand feet twice during the flight. Apparently, while the captain left the cockpit for a moment to use the restroom, the co-pilot accidentally pushed the aircraft controls with his knee while adjusting his seat, causing the airplane to move in an undesirable way. Meanwhile, the captain tried to go back to the flight deck, but found the door securely locked. (read the news here and here).
Could you open the door, please? (making a request)
Are you able to open the door? (asking for information)
I need you to open the door now. (expressing need)
Open the door! (giving an order)
If I were you, I would open the door! (giving advice)
If you don’t open the door now, you will be fired! (making a threat)
You should have opened the door… (expressing regret)
If the correct grammar structures hadn’t been used (modal verbs, conditionals, imperative, etc), there would be no way of expressing such different meanings!
So, consider grammar as a tool that is at your service, just to help you say what you want to say. The better you use it, the better you will communicate. And who doesn’t want to communicate well?