Like AMJ I also addressed every part of the question. However I focused primarily on what I have done up to this point, mentor underrepresented minority high school students, because I felt that provided the most tangible evidence of commitment to the CGSM mission. 2/3 of my essay.
Other 1/3 was about helping students applying through the consortium by offering advice on the process, either as a CGSM liason or through diversity coffee chats during breaks and participating in the CGSM alumni organization after graduation.
I would guess the most important part is discussing your commitment sincerely and honestly. The letter of recommendation for consortium membership likely is also used to give your essay credibility.
OnePlusOne
For those of you who have been awarded fellowships, how did you demonstrate your commitment to the CGSM mission?
Good question, and good on you for asking!
I was able to think through the CGSM Membership question in the three steps they asked us to consider:
Step 1: What have you already done before school.
Step 2: What will you do while in school
Step 3: What will you do after school, once you have the degree.
For me, the "before school" part was fairly straight forward - tutored this kid, mentored that kid, was VP of this club in college and Prez of that org after college, etc.
The trickier part was suggesting what I would do while in school. I researched the diversity outreach opportunities at the schools I was applying to, and did a bit of a strategic exercise to determine where I thought the holes were, and how I'd be able to fill them. It's sort of an idea-generation ask from The Consortium - they want to know how creative you'll be in really putting in the time and effort to reach out to and recruit minority students like yourself into your MBA program and specifically into The Consortium.
For step 3, I chose to play on some of the groups I already participate in, denoting that I'd stay involved in those groups post-MBA but I'd also contribute XYZ as a result of having the MBA degree. For example, if you want to work in finance post-MBA, let's say, it might behoove you to express interest in mentoring awardees of the Toigo Foundation's scholarship or something like that. Naming other diversity organizations isn't a detriment to CGSM membership, as they partner with many of those organizations that serve the same purpose as they do.
Perhaps just approach the membership essay from a 30,000-foot view first, and then get specific, as the specifics on how you'll make a difference are what they're looking for.

Good luck!