From its beginning Christianity had to deal with those in the community who zeroed in on the intellectual dimension of their faith and ignored the actions which Jesus expects his followers to perform. As long as they believed in the salvation which Jesus' death and resurrection offered, they thought they didn't have to imitate the concrete actions of the historical Jesus which actually brought about that salvation. For the rest of their lives they could simply lean back in their recliners and "believe."
Luke didn't want anyone in his community to become "minimal action" Christians. That seems to be why, throughout the initial chapters of Acts, he inserts short narratives describing how members of the early Jerusalem church channeled their faith in the risen Jesus into specific acts of love.
"The community of believers were of one heart and one mind. They never claimed anything as their own. Everything was held in common . . . there were no needy among them . . . . All who owned property or houses sold them and donated the proceeds . . . to be distributed to everyone according to their needs."
Luke is convinced that believing, life-giving communities exist only because their members are willing to die by generously giving themselves to one another. People's needs can only be taken care of if someone gives part of himself or herself to make up for what's lacking in the other.
According to those who study John's gospel and the three letters bearing his name, the publication of a gospel which constantly stressed faith in Jesus as God opened the door to those who thought they could be saved by what they believed and knew instead of how they loved and sacrificed themselves for others. They rejected the life-giving tension which develops when someone both believes and acts, exchanging it for the false serenity which comes from just believing Jesus is Yahweh.
The I John author tries to counteract this tendency by stressing how our knowledge of the relationship between Jesus and the Father should prompt us not just to ooh and aah in amazement, but to "do what God has commanded." We're expected to conquer the world. But we can't do this by just meditating on the intellectual ramifications of Jesus' divinity. We must also reflect on and imitate the things he did for others. That seems to be why the writer contrasts "water and blood." It's a reference to Jesus' baptism and the blood shed in his death.
Though there were misunderstandings about his gospel, John the Evangelist never let his community overlook the dying aspect of Jesus saving us. Most of us concentrate on the "doubting Thomas" section of today's pericope. We smile at someone so sure of himself that Jesus is dead that he has to eat crow a week later when the risen Jesus stands before him.
It's important to reflect on the criterion Thomas employs to prove the person in front of him actually is Jesus. "Unless I see the mark of the nails in his hands and put my finger into the nailmarks and put my hand into his side, I will not believe."
Notice during Jesus' first visit he breathed on his followers and said, "Receive the holy Spirit. Whose sins you forgive are forgiven them and whose sins you retain are retained."
It doesn't take a lot out of us to "retain" someone's sins. We keep them in mind, use them in our evaluations, and contrast them with our own "sinless" personality.
Those who forgive die to themselves; they destroy the power which retaining gives them over others. Forgiving wounds us. But like Jesus' wounds, they take away other people's pain. Only such wounded Christians can legitimately believe in the salvation which Jesus offers.