The Noun-Verb duality.

Matter or energy,
Wave or particle,
Zermelo-Fraenkel numerals or Church numerals,

You can see something as a being, or as a doing.

Think about it this way.

You can have two pennies in your hand. But you can also jump up and down twice.

Yet, we can still use the concept of the number "two" to relate both of these situations, even though it describes two things in the first case, and two instances of an action in the second.

Isn't that interesting?