What he means by this is that everything that exists can be given a place in a great pyramid like structure.
All the things at one level exist because they play a role or they have a function in contributing to the well-being or others.
But existentialists deny this thinking of Aristotle or any other thinking that believes in god or fate.
As they deny that God and his fate is playing a role in how he places an order in the world.
They say that nothing occurs for a reason or that everything doesn’t happen for a reason.
As for example they believe that if you lose your job this is a particular event in its own term not because you may get a better job.
Or because this job loss would lead you to a better fate because that is what God has destined for you.
Nothing the world is nothing or in other words the world has no order or logic in place to place upon it.
For example also some existentialist especially Friedrich Nietzsche said:
That it is painful for humans not to place order and purpose for their lives and for the world.
As they have the desire to do so because otherwise they will feel the agony and pain of not doing so.
And this agony and pain comes from the discovery the meaningless of life.
Which this view is totally atheistic because if you believe in god whatever your religion is.
You will believe deep in your heart that everything in the world happens for a reason
And that everything in the world has a purposeful function.
And this is what I personally believe too.