John's foundational premise is that children share the nature and likeness of their father. This is true in the natural realm, but also in the spiritual realm. Though every human being is a child of God as a creature bearing the divine image, the fall established a new fatherhood to which all people conform as -image-sons.- In their natural state, all are children of the devil, and become true children of God through union with the unique Son. In this passage, John discussed how a person identifies which father is his own.