Reasons for doing a masters in maths [on hold]

I am a current 3rd year undergraduate at University and I am thinking about doing a msc degree in pure maths. To those that have done a masters in maths, what were the main differences between undergraduate and postgraduate study? Did doing a masters develop you more as a person? If so how? What did you most enjoy about doing a masters in maths? I am interested in hearing people views.