All pages have one fixed place in the information architecture, which you can visualise as a tree structure:

Usually, you can see the information architecture of your website in the structure of the urls. The branches in the tree are the folder names: https://www.ru.nl/niveau1/niveau2/pagina-op-niveau3.

The menu on a site is also based on this information architecture, although sometimes a menu only shows part of the tree structure. For example, the hamburger menu on our site only shows the top 3 levels.

The left menu on our site currently shows a selection from the information architecture: up to 3 levels, depending on how far you have clicked through in the tree structure.

There are two things that visitors must be able to discover independently in order to successfully use the website:  

1. What content is there on the site?  
2. How can I navigate there from where I am now? 

So the website will have to communicate both of these things to the visitor, in different places in the website. 

It is therefore important to communicate (part of) the underlying structure of your site to your visitor. This way, a visitor can assess which content can be found on the site and you create a sense of place. This is important, because visitors need to know where else to go if the information on the current page is not what they are looking for.  
Not all visitors navigate neatly from the homepage, through the path we have laid out for them, to the right content. Firstly, they may come for a non-topic task and so there is not a very clear path. Then they have to look for the desired information themselves. Secondly, a visitor may land from a link or search engine, in the middle of our website, or jump to any page in the website via the internal search function. At that point, the visitor then does not know how the page is related to the other information on the website.