Consider the hierarchy of the Aristotelian causes in the order of increasing dignity:
For prime matter, its material cause is within it; all other causes are outside. This includes even the efficient cause, because prime matter does not “work” or function in any way; it’s completely inert. Someone else must make quarks and electrons with it.
For merely material objects, their material and efficient causes are within. When we ask, “What makes this car exist right now?” the answer is, “The fact that it’s made of such and such materials and works in a certain way.” However, the car’s final cause is outside of it.
A machine has no purpose other than to serve man by performing a useful function. Its “goals” do not differ from those of its creator. It wants nothing for itself. It is a perfect slave. A human slave might try to hide his abilities so as not to be swamped with hard work; a machine would not “think” of anything so clever. Or, a master must make sure that the slave will prefer to comply with the master’s orders over rebelling; a machine does not in this manner calculate benefits and opportunity costs. A machine has no internal life or experiences that are inaccessible to anyone but itself. Where the machine ends and raw materials and the environment begin is an arbitrary decision.
For humans, now also their final cause is within. A man’s purpose is his own happiness, his own joy. He is essentially no one’s tool, though of course people do make use of each other, say, in the market or within a firm. A human being is an end in himself.
However, a man’s formal cause, i.e., the answer to the question “What / who am I?” is still external and will only be revealed to him upon entrance to heaven in glory: God “shall give him a white amulet upon which is inscribed a new name, which no one knows except the one who receives it.” (Rev 2:17) Even then, we will be what God makes us into. In order to find out what a person is in all his unique individuality who is in the process of becoming, we’d have to query God and His mysterious designs.
Lastly, God has even the formal cause internally. He is 100% what He is, complete and perfect.