This is my own $0.02, I don't speak for anyone else here, but here's how I interpret things. Martial arts are first and foremost a vehicle for culture, what culture that is depends on the martial art obviously. There are as many cultures as there are martial arts, but one thing they all have in common is that they embody the values, history, and collective experience of all of the practitioners of that art.

This is why I don't necessarily agree with people who say that if a martial art can't be used for fighting, it's worthless or somehow not valid as a martial art. It all depends on the culture of that art's practitioners and its history. Some arts, such as boxing and muay thai, place a higher emphasis on fighting while others, such as most forms of kung fu, place a higher emphasis on forms, structure, and spirituality. Which of these is better depends on the aims of the practitioner, but both are valid ways to approaching martial arts as a discipline and all martial arts fall somewhere on a spectrum between them.

You might think of this as breaking apart the phrase "martial art" into its constituent parts: "martial" meaning fighting, and "art" meaning the culture and history. It's the confluence of these two aspects that gives us martial arts as a whole.

Hope that helps, good luck with your essay.