Being invited to attend an interview indicates that you are a good match for the job specifications that the employer has set out. However, at this stage, that match only looks good on paper; the interview is your chance to convince the interviewer that not only would you be able to do the job, but you would also bring additional benefits to the organisation.
The interviewer will probably have to see a number of applicants; the ones that they remember will be the ones who are distinctive and can make a unique contribution to the organisation. So to be successful, you will need to be different and make a firm impression. In order to achieve this, it's essential for YOU to know what makes you unique, and what makes you the best candidate for the job, so that you can convince the company to invest in you.