Gulli
It is quite difficult to produce documents for you in answer to that Assignment question. The first part of it is subjective; asking what you see (your opinion) as the main purpose. You need to justify and evidence any statements that you make and that is where your research will come in. Unfortunately I can't do that research for you, otherwise your work will have little depth to it. The questions that you should ask yourself are:
What do I understand security management to be?
What is security management designed to protect?
What is its context - does it stand alone as a management function? Is it business integrated?
What do organisations require from security?
Also, you may need to research wider - not directly security - management principles and theories
Considering the threat and commensurate measures, you should perhaps look at the principles of threat and risk analysis,; characterising/understanding the organisation and assets to be protected. Consider also the issues of cost/risk balance and analysis. Again, it would be useful for you to research issues of organisational context.
Think also about enterprise risk (the risks that competitive organisations take to remain competitive), risk appetite, risk perception and board-level engagement. Commensurate risk mitigation would also be a useful term to research.
There are very many texts, white papers, book extracts and documents available through multiple web sites - you could also look for case studies. The vast majority of this will be available to you without leaving your keyboard!
I strongly advise you to do this research to develop your understanding of the subject area. You should develop a picture and basis for your work that illustrates your understanding of the needs of the organisation and the requirement to provide balanced and effective risk management and security implementation process - security is inconvenient to many and implementation of inadequately thought-out processes does little to integrate and thus enhance overall organisational effectiveness. In the main; the aim of all this is to protect the organisation's bottom line - its profitability.
I hope that this helps.
Regards
Archie