Question about "the world" according to Sokolowski's Introduction to Phenomenology

Hi. I'm having a hard time trying to interpret the following passage of Sokolowski's Introduction to Phenomenology, Chapter IV:

So there are many things in the world, all given in different manners of presentation. There is also the world itself, which is given in still a different way. The world is not a large "thing," nor is it the sum of the things that have been or can be experienced. The world is not like a sphere floating in space, nor is it a collection of moving objects. The world is more like a context, a setting, a background, or a horizon for all the things there are, all the things that can be intended and given to us; the world is not another thing competing with them. It is the whole for them all, not the sum of them all, and it is given to us as a special kind of identity.

The entire passage seems kinda cryptic to me, specially when he says that "[the world] is the whole for them all, not the sum of them all". I have no idea how to distinguish "the whole of them all" and "the sum of them all". If anyone can help me, I would appreciate.