There used to be a saying of philosophers: "Anima est quodammodo omnia."
We can see the truth of this by considering what St. Thomas calls the two types of perfection. In things, perfection may be had according to the act of existence. Inasmuch as a thing is what it is in virtue of its species, it possess a sort of existential perfection. This type of perfection, though, is not absolute since it may be found in many things. The perfection that follows from the act of existence in a created thing is always distinct from the perfection in another. In this way, even the perfection of individual things is imperfect since individual things, through their perfection, are only parts of the perfection of the universe. We can see, then, that creation is both perfected by being what it is and imperfect by being limited to itself and not found in another.
This is overcome by the second type of perfection. This perfection is not found within the act of existence but is somehow found in another. Just as something has perfection by having the act of existence, this perfection is achieved through the possession of some act, albeit not the act of existence. Through this type of perfection, then, there is a way in which the perfection of the entire universe can be found within an individual thing.
The thing's name? Man.
That by which he possesses all perfections? Knowledge.
"The soul is, in a way, all things."