Grammar and punctuation corrections are in green. Corrections in blue are suggestions and are up to your stylistic preferences.
I have a weakness for smart, funny, and inspirational YouTube videos. My favorite is the "You are Not Special" Commencement speech given by an English teacher named David McCullough. During his speech, Mr. McCullough urged his students that whatever they do in their lives, they do it "because you love it and believe in its importance." Ever since I heard that speech, I brushed aside all thoughts of majoring in biology or engineering, to focus on my most intense intellectual interest: economics.
My interest in economics started when I was a small boy living in a large apartment building in Brooklyn. While I was growing up, the predominately Irish and Italian neighborhood I lived in saw an influx of Arabic, Russian, and Chinese immigrants. I was amazed by the differences in culturedifferent cultures of my new friends and neighbors, but even more amazed by the incredible food inserved at the new falafel restaurant on the corner and sold at the Chinese grocery store across the street.(This sentence is a bit long. Consider breaking it up?) Living in that neighborhood made me feel like I was watching the world move in fast-forward by some sort of magic.
I realize now that the magic transforming my neighborhood was the unseen forces of economics. (Please elaborate. Just an example, even the most basic idea like coincidence of wants, etc will work) My love for economics stems from the fact that these forces have not only transformed my old neighborhood, but have also shaped human history. The world we live in is a result of a long story of economic development. Today globalization has put us in a particularly interesting chapter of the story, where emerging economies can triple their GDP in a decade and everything from the shirt on your back to the food on your plate traveled thousands of miles to get there. Studying economics helps us understand how this new globalized world works.
I believe economics is important because it ultimately boils down to people. After all, economics is the study of the production, distribution and consumption of goods and services that are used by people. We are all economic(Omit, implied) actors in a world where a slight increase in interest rates or the national debt affects the lives of millions. All economic(a new word would be nice. fiscal?) decisions, whether made by governments, businesses, or individuals affect the outside world. I want to study economics because I want(Works without it) to understand how my decisions both as a businessman and as a person impact others.
Studying at Cornell would put me in an intense intellectual environment, inhabited by inquisitive students and renowned professors. While the diverse range of classes that Cornell offers in its College of Arts and Sciences will allow me to become a well-rounded individual who'll be able to handle life's challenges and give back to his community. (This sentence needs to be rewritten. It's too long and is an incomplete thought since you began it with "while.") My personal goal is to gain a PhD in economics and become a professor. I know my goal(this ambition? another word) will be aided by the great faculty and immense research opportunities at Cornell; (Semi colon or period.) I just hope my weakness for YouTube videos won't get in the way.
For me, the strongest parts of your essay are the anecdote from your childhood and introduction. The part about economics tends to be slightly wordy and redundant. I'd add references to solid, real world examples, personal experience or theories to support your intellectual musings.
The rest has been commented on by everyone else, especially HarvardAccept (funny name, btw). Good luck on Cornell!