Is the purpose of grammar to make English behave like Latin?
The purpose of grammar is to make English behave - to make it comprehensible.
Grammar is the set of rules a language operates under, including but not limited to punctuation, syntax, word usage, inflection, etc.
So why is grammar important? Because without rules, we wouldn't have a language - instead we'd have an incomprehensible set of sounds and words that make no sense. Much like rules are needed for driving on a road (otherwise you end up with vehicles going wherever, however they chose), rules are needed for language.
With grammar, you know that at the end of this thought that I am currently writing, there will be a period to let you know that I am done with that thought and ready to move on to another.
But without grammar I could just keep on typing and not letting you know when the thought is done in fact i can even drop commas to remove pauses and breath spaces and even stop capitalizing altogether or capiTalize ranDomLY simply because i CAn&
Which is easier to understand - the one with proper grammar or the one without?