Why is a good theme important for your wordpress website?
The quality of a wordpress themes or templates is an extremely important factor which they work very hard on improving. It's not hard to see why - when people look at wordpress templates they see what their potential website could look like, which is extremely important for the obvious reason of if you feel as if your website is going to look unbelievable using one brand and okay using the other, your decision is made. That's a reason why a good wordpress theme is important for your site, not just from the seller's side. If you see the website of your dreams is only a few text and picture changes away, you are going to be far more motivated to get it up and running. Motivation is extremely important when building a wordpress website, as making one successful is a marathon and not a sprint. Without motivation, consistently creating content and testing out new things with your website is going to feel like a chore!
Also, good groundwork makes for a better chance of building a good wordpress site - If what you are starting with looks usable, clean and modern, then the likelihood is that the final product is going to be the same (or better), regardless of who is developing it! For a lot of people, getting a wordpress website which looks like it was made professionally seems unattainable, but with a good template and some simple changes, it's really not very hard at all!
Some wordpress themes are also great for design ideas. Some wordpress sites have a set of templates of which the number extends in to the thousands, so there are guaranteed to be some great features for you to pick out to implement in your own wordpress site.