In general, getting an invite to serve involves you (or rather, your application) going through several 'filters.' When you apply your name goes into the pool of possible candidates (with the new system, for that specific post). When it come to actually choosing who will go, they will filter the pool down by a variety of things, like educational background, relate-able experience,volunteerism, etc. The best rise to the top of the pool and are more likely to be chosen sooner.
Along with that 'hard' data, the placement team looks at things like what your references said about you and, now, what you said on your Soft Skills Questionnaire. These final things, along with interviews etc, are used to get a feel for who you are and weather you are 'right' for the program.