Shri Nathji often told the story of the two artists who were provided two opposite walls on which to exhibit their art.
The first artist painted a picture on his wall.
The second rubbed his wall continuously, polishing it till it shone like a mirror. In this mirror was reflected the handiwork of the first artist.
Whilst the first had laboured and toiled at his art, the second had cleaned and polished his wall. The net result of the two was the same.
When a man so purifies his heart that it becomes as clean as a mirror, when it is freed of all desires, anger, greed, hatred, lust, fear, when man has the Glory of God within it, then all the knowledge of the world appears in it like the reflection within a mirror.
Since Shri Nathji was God Himself, this came very easily to Him. God was All-Knowledge.