They're asking for 600-900 words, whereas you hit almost 1200. So, you need to shorten this by quite a bit. Fortunately, there is quite a bit you have that can be cut without hurting your application.
For instance, your first paragraph essentially says that you are an economics student who is interested in economics. Your application for a MSc in Economics sort of makes that self-evident. You could probably reduce that entire paragraph to a single sentence, if not cut it altogether.
taking in contemporary works like Adam Smith's "The Wealth of Nations"
Um,
The Wealth of Nations was first published in 1776. It is not therefore "contemporary" by any meaning of the word that I know. It could, however, be described as "modern," under some definitions of the term, though even that might be confusing.
Not studying economics as a subject no longer seemed an excuse for me to actively read up on the subject.
The two negatives here are confusing, and I am not sure that the sentence actually makes sense.
Most of your fourth paragraph seems eminently expendable.
I have thought long and hard about what lies ahead in the short-term and long-term for me.
As are sentences like these.
Overall, then, your essay is fairly solid. Cut it down to about half its length, trying to fix minor errors of the sorts I pointed out above as you go, then repost for more feedback.