A cover letter acts as the link between your resume and the job you are applying for. It is meant to help express your interest in the job by selling yourself. A statement of purpose, i.e. SOP, is actually a concise essay, usually of 2500 words, which is meant to portray your value to the organization you wish to join. It should ideally contain all about you – who you are, your weaknesses and strengths and why you believe you are the most suitable candidate for the specific job or internship. Your SOP should be well-organized, systematic and earnest and professional.