Based on several sermons, Natural Theology is an argumentative piece that explains the absolute existence of a deity of God based on the common knowledge of mankind.
Paley's first analogy is that of a watch being made, and how that relates to human thoughts on the unknown. People that buy watches don't really know how they work, have never seen one made, and the watch has functions that are practically unknown. Although this is a very biased an haphazard analogy, Paley connects this to religion in that, even though a watch is one of many possible material combination, we know it is there even though we don't know how it is made. The same, he argues, is true of a God - we don't know how it works or is made/makes, but we know - or, should know - it is there.
Paley continues on the topic of a watch, explaining that the maker of the first watch has now made a second watch. In a way, the first watch reproduced itself, using the watchmaker simply as a vehicle for creation. In the same sense, he says, a person makes a water mill, and the mill grinds corn. The water is what is grinding the corn, but a person simply made the mill so that the water would have a vehicle or medium to grind the corn.
Paley argues that the same type of thing can be applied to the rest of the world and to nature - things are built by design to have some meaning or purpose in society. While it is true that these things may not be alive, one might not know exactly how they work, just like one does not know how a deity works. Paley's conclusions are perhaps outdated, as scientific evidence has come the its own conclusion on the topic.
