First impressions count!
You have managed to get someone to your site, either they have been told about you, they have googled you or they have seen your web address on your van or an advert. So what is the first thing you want them to see?
Some people look at me strangely when I say that the main purpose of the opening page of your website is to get rid of most of the visitors. Yes, it does sound a little insane, but you do not want to deal with everyone in the world. You only want to deal with your target market.