Though he does not mention it explicitly, John begins his gospel with the cross. He looks ahead to the cross as the light’s decisive victory over the darkness. The darkness will seek to destroy the light, but the light will not be overcome(1:5).
These cosmic entities of light and darkness are not just abstractions for John. They are human characters. Jesus is the light and Satan is the darkness. Jesus is life, Satan is death. The setting is likewise not some cosmic plane. Our own world is both the stage in which they do battle and the prize for which they fight. Jesus, the awaited Messiah and rightful king of the world, has overcome the present “ruler of the world.” The darkness has been lifted.
As Jesus’ time draws near, he speaks to his disciples of the fate of the current ruler.
“Now is the judgment of the world; now the ruler of the world will be driven out. And I, when I am lifted up from the earth, will draw all people to myself.” He said this to indicate the kind of death he was to die(12:31-32).
This casting out of Satan is the reason Jesus has come into the world. In defeating the one who holds the power of death, Jesus himself will seize eternal life. Death will no longer have any authority over his body.
It is this defeat of Satan that allows John to write of the cross as being for others. Everything Jesus gains, will be declared to those who believe(16:15). In attaining eternal life then, Jesus gives eternal life to those who believe. Jesus bears the cross so that all people might obtain eternal life(3:16).
For John, the flesh of Jesus is a necessity for this imputation of his eternal life to others. Jesus’ victory is of no use to flesh and blood if he himself is not flesh and blood. His body and our body must be of the same kind for us to receive his eternal body.
This is the primary way in which the writer understands the cross. Jesus has defeated the one who holds authority over death and in doing so achieved an eternal body. Any who eat of his flesh will receive the body that Jesus won(6:51).