As an applicant myself, I'm not sure if I'm the best to evaluate this but i will try. Overall, i think you have a very good essay but struggling with a just a few punctuation and putting the message across.
... in Nigeria
, - have deepened...
embraces my yearnings, which ... with regards to ... security
-, a major ... sector and indeed world over.
Also, i think your essay lacked how the courses will help your future career. If you look at the marking procedure, it says "Applicant clearly demonstrates that they have thoroughly researched their three chosen courses. They provide excellent and detailed arguments on the relevance of the master's program to their future career and the development of their sector and country.
You might want to have sentences like: "The MSc in xxx programme at the University of xxxx will equip me with analytical, problem solving and research skills to design innovative impact-based strategies to the multifaceted challenges of xxxx interventions in Nigeria. My experience working with various xxx stakeholders have exposed me to the disconnection between Nigeria's xxx policy initiative and implementation. This situation is attributed to inadequate professionals and lack of expertise in impact assessment and evaluation, to leverage on timely, accurate and relevant data to inform evidence-based implementation. However, with applied knowledge from modules such as evaluation methods, community analysis and critical appraisal at Oxford, I hope to build the needed professional competence to improve data management system in Nigeria".
This might be wordy, just play around the words and develop a better research into the course and how it helps you and Nigeria. You might also want to scrap your experience bit in the second paragraph and then introduce them here.
All the best Daniel!