The job application letter's sole purpose is to get the recipient to read your CV. It should be clear, concise and straight to the point. Here you are simply telling the employer that you are worth having a look at.
The application letter should be brief, no more than one page in length. It should be easy to read and flow through. It should include only the absolute necessary information. Like most other things, there is a formula that works extremely well for preparing job application letters.