The most important feature in language comprehension

When first asked what the most important feature is in language, I thought vocabulary. If you don't know the words, you can't communicate, or so I thought originally. But then I went back and thought about how babies communicate and how non native english speakers communicate. At least for me, no matter how many vocabulary words a person knows, if I can't understand them, then it doesn't matter. However, someone who knows very few vocabulary words but has the proper sounds and syntax can sometimes be understood more clearly.
One thing that stuck out in my mind when thinking about this was one of my trips to Egypt. My mom does not speak Arabic, but she learned a few words, but has a very limited vocabulary. She practiced the few words she knew and learned how to enunciate them properly. She also learned the context and proper syntax of the words she knew. She would go to supermarket there and get by on those few words and communicate effectively. I do not think they same thing would be true if she just knew a lot of words, but could pronounce them properly or said them with incorrect grammar.
So, I narrowed my answer down to sounds and syntax, which I think are more important in language comprehension. Of these two, I would say sounds is the most important as evidenced by a few other examples I have seen. Often, I can understand what someone is saying, even if the grammar and syntax are awful. But, as seen in the compilation of my notebook for this introseminar, a few changes in the sound of the words sometimes makes it impossible to recognize the words being said.
In the end, I think that sounds are the most important feature of language comprehension. Without sound, I do not believe that syntax or vocabulary are entirely relevant, it begins with sounds.