-This paragraph is mostly unnecessary. Saying that you have the intensity, persistence, knowledge etc. means very little. Showing it is what an SOP is all about. The last sentence should absolutely be removed: their program is obviously designed to produce mathematical scholars and saying that you "hope" it will do so it a little strange.
-It seems to me that this paragraph would be much more forceful if you elaborated on this paper you wrote and explained, in depth (for that is the major thing this SOP lacks), what you loved about it. What, specifically, interested you? Can you pursue the same (or similar) lines of inquiry in other instances? You give no specifics which compromises your ability to demonstrate depth of knowledge and careful consideration of your interests.
-You do not have to pursue the area of interest you adopt in your SOP, but this sort of generalizing could easily portray you an uninformed and superficial in your pursuit of graduate studies.
-If you love your job so much, why make this sort of career change? What's missing from your career that would be fulfilled by grad school? I'm not sure what your goal is with this paragraph. Again, you are saying how prepared you are without showing it. Why should they just accept everything that you claim here?
-This paragraph is not a good idea. It basically shows that you are not serious about academics. Change this to say something about the determination necessary for completing your degree, its importance, how it didn't complete your education but motivated you to continue it.
- So, you end this SOP by claiming that you've made this decision carefully. You need to demonstrate this - explain how your current situation is insufficient, what you would like to do that you are currently unable to (and "doing research" is not specific enough).
-Also, they know that they have a strong mathematics program that enables graduates to do research, so why are you telling them this?
-I think you've gotten off on the wrong foot here. My suggestion would be to concentrate on developing a specific set of questions which you would like to pursue. A good way to do this is to expand on the paper you mentioned and reveal what it was that interested you so much. Also, use your work and educational experience to explain why what you've done isn't sufficient. What, specifically, makes you want to trade your current life for an academic one? Your statement is so general it makes it difficult to believe that a) you really are interested b ) you know what you're talking about and c) that you've considered this choice carefully.
-I don't want to be so critical but you hint at a few things that could be very productive for you in this essay (your work experience and drawn-out education) but you don't use them effectively.
All that said, I'm not at all familiar with mathematics, but you need to focus on including more specifics, and showing what a great candidate you are, not just saying it.
Good luck! and don't be discouraged. These things are very hard to write!