“I do not know what anything is for.”
You feel responsible for your presence here and have, mistakenly, concluded that the reason for that must be that you created yourself. And since you obviously did not create all that you perceive in your environment, you stand separated and alone. You find yourself looking at everything, rather than with everything. And that is why you do not really know what anything is for. Let’s look at the distinction between at and with a little closer.
Your imagined separated position induces a state of mind that is constantly trying to justify itself. This state of mind looks at the outside world and assesses it in terms of how useful a given person, thing or situation is in light of your need to justify your existence. That explains the word at in: … looking at everything, and judging it.
But you do not have to justify your existence at all. God created you as part of Creation. You are part of the whole. That explains the word with in: … looking with everything, and accepting it all as Life in extension.
From the perspective of the living whole, everything serves the purpose of its own well-being. Since you are (part of) the living whole and were created by it, everything serves you. That is why the lesson says: “Everything is for your own best interests.”
Your sense of identity, and thus your agenda, determines whether you judge everything or accept everything.
Full text of Workbook Lesson 25 in ACIM