The Gospel of John is the gospel of the spiritual rebirth, of the Gnosis and the eternal life, this gospel unlike the Gospel of Luke and Matthew does not contain the beatitudes of Jesus but this Gospel describes the spiritual rebirth through Gnosis, in the dialogue of Jesus with Nicodemus, John 3 and it is also the only gospel that explains to us what is the eternal life. Gnosis is the philosophical expression of "receiving the holy spirit." The Gospel of John is the most Gnostic, and the most mystical gospel. In this dialogue with Nicodemus, Jesus narrates the struggle between light and darkness and affirms:

Everyone who does evil hates the light
and will not come into the ligh
for fear that their deeds will be exposed.
But whoever lives by the truth comes into the light
so that it may be seen plainly that what they have done in the sight of God.

 Jesus teach to us in his dialogue with Nicodemus that there are two ways of acting. Truth and falsehood are concepts before of good and evil, are the last substrates.
We love the truth or the falsity of thence we are good or bad.
The truth is intimately associated with the light of wisdom and knowledge. If we practice the falsehood, we practice the error and lie, and their return is death.
However if we practice the truth, this will return us peace and the perfection of life. Recall that the characteristics of the truth are precision and accuracy. If we, in the front of the problems, we target point , we minimize the error and therefore the suffering, we reap life.
The common good is born of the truth. A society where people practice falsehood is a society of criminals. And more; crime is the most distinctive factor of falsehood. Common good or crime, life or death; against these elections we are when we practice the truth or the falsehood, this is the fundament of the fight between the light and the dark in the gosple of John.