Why did the Athenians Paul preached to know nothing of the true God?
The Athenians knew nothing of the true God because their worship was idolatrous, filled with many gods and goddesses. Even their altar to the unknown God was a precaution in case they had missed one. They did not know the God of creation.
Les teaches that Paul was ministering among people whose new religious ideas were only another rehash of an oriental god or a mythological goddess imagined on some mountaintop. They knew nothing of the true God. Paul observed their devotions, meaning their idolatrous worship, and found an altar inscribed "to the unknown God." Les illustrates this with a man who told him to pray to St. Jude and said he believed in plugging every hole. Similarly, the Athenians had all their gods and goddesses, yet in case they were missing one, they set up a special altar to the unknown God. They knew nothing of the God of creation.
Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come: