1.
I felt that I just had to get through the class and never come back to the boring subject again
2.
During the first half of the course I was very confused and didn't really understand many concepts and things I was hearing in class.
3.
I spent more time than average of what I spent for any other of my classes and still didn't understand the material.
4.
The choices for my profession have always been changing.
I understand that you want to put across the struggle you've had in the past with the subject and that you wish to rise to the challenge, but I believe the statements I've quoted above do yourself a great disservice. You are, perhaps unintentionally, revealing negative traits about yourself and need to address them.
Referring to the quotes above:
1. Though you're talking about the past, you're still putting across the idea that you found it "boring". Admissions tutors are more likely to pick someone who has always been interested/captivated by the subject.
2. Suggests you may lack the ability to succeed and are likely to struggle on the course.
3. Like #2, it may cause the admissions tutor to cast doubt over your ability to keep up with the course material.
4. This creates uncertainty over your intentions for study. Admissions officers may be thinking to themselves "Does this guy really know what he wants out of this? How likely is he to change his mind mid-course and drop out?"
I hope you can see where I'm coming from. I'm being necessarily critical as this is the best way to improve your application.
I would remove the negatives and try to always focus on the positives. For instance, you could talk about how you've always been interested and found the material to be challenging at first, but through hard work and dedication you have overcome your past failures and this convinces you that you can succeed in this field. Make them feel as if they you've always wanted to be a taxation expert and that this is your life's calling.