Content is King. It is what makes your site special and attractive for visitors.
It is vital that the content is made accessible such that no one is excluded from gaining benefit from it, and so that you reach the widest possible audience.
Don't panic - achieving accessibility is relatively straightforward. Much of this will already be familiar.
In essence:
Content should be specifically written or modified for the web
Content needs to be simple, clear and easily scannable
Content needs to be structured and consistent between pages
Images need to be used wisely and it is vital that alternative text descriptions are provided for those who cannot see them
Data tables need to be as clear and simple as possible
Extra information about each page should be provided