A quote can be useful for your P.S., depending on how it will be used and how relevant it is to the rest of your essay. But, I think you can also do well w/o it. I think the adcoms will appreciate more about what you have to say, in simplicity and honesty, vs. a quote that might be interpreted more than one way and hence, maybe the need for a more detailed explanation, which might shift the reader's attention somewhere else instead of being on you.
If it flows well and it is not distracting, then use it. If not, just normal sentences will do. Just my 2cents.