We know from Paul's letters that things weren't always as peaceful and well-ordered in the early Christian communities as Luke implies in his Acts of the Apostles. Thankfully today's first reading gives us a hint that everything wasn't always copasetic, even in Acts.
First, not everyone trusted everyone else. No matter his life-changing experience on the road to Damascus, Saul's motives in joining the Jerusalem church are still suspect. Though we presume each member of the community had gone through an adult conversion, they didn't trust what some others said about their own conversions.
Second, not everyone agreed on the way their faith was to be shared by others. Being a Hellenist - a Jew raised in a Gentile environment - Saul naturally reached out to other Hellenists, with disastrous results: they put a contract out on him. No doubt there were individuals in the community who observed, "Things were calmer here before Saul arrived."
Third, things did get calmer after they sent Saul to Tarsus, far away from Jerusalem. It seems not everyone could be integrated into every Christian community. In spite of Barnabas’ intervention, as long as Jerusalem Christians limited their outreach to other Palestinian Jews, Saul was more a problem than a gift.
Perhaps that's one of the reasons the author of I John encourages his readers, "Children, let us love not in word or speech, but in deed and truth." It's far easier to keep a church together when its members just talk Christianity than when they live Christianity. Believing in the name of God's Son, Jesus Christ is relatively simple and non-divisive. It's when we love one another as he commanded that we run into problems.
Because no one specific action always shows love to everyone all the time in every place, we can have legitimate disagreements on how we're to imitate the love of Jesus in the concrete situations we encounter every day of our lives. One gives oneself for others in one way, someone else in another way. Yet no matter how we love, our goal always is to "remain in him . . . the way we know that he remains in us . . . from the Spirit he gave us."
That seems to be why John the evangelist has the soon-to-die Jesus stress the unity he expects his followers to have with him. "Remain in me, as I remain in you. Just as a branch cannot bear fruit on its own unless it remains on the vine, so neither can you unless you remain in me. I am the vine, you are the branches."
We're one with the risen Jesus not just when we feel comfortable in our faith. We're also one when, like Jesus, we're reaching out to others. We can identify with his pain and joy because in trying to copy his behavior, we experience the same pain and joy. We're one with him not just in faith, but also in action, even if at times our actions create problems within the community whose faith we share.
Luke presumes his readers know that Saul's interaction with the Jerusalem Hellenists prefigures the direction the whole church will eventually take. As disturbing as it was in the beginning, that was the direction which eventually produced the fruit of Gentile conversions which all Christians take for granted today.
It's important to note that the only branches which are lopped off the vine are those which produce no fruit. Perhaps the "pruning" Jesus refers to - the pruning which always produces more and better fruit - comes from the very tension arising in Christian communities when all their members actually try to live their faith.