In today's Gospel, Jesus uses a agricultural metaphor to talk about the Christian life. He is the true vine and we are branches. We grow as we take his life into ours. Branches cannot survive without the vine. Cut off from the vine, they wither and die. Around my house we have wild grape vines. They grow everywhere! As they climb other plants and trees, their tendrils grab hold. The only way to disentangle them is to prune them, cutting the branches so they are no longer attached to the vine. Once they wither, they're much easier to pull off.
What grows on vine? Grapes. My grandmother used to make grape jelly from the wild grape vines. Saint John uses this story of vines and branches to talk about Christian living because of his theme of the Eucharist. Remaining in the vine, refers back to the Bread of Life discourse in chapter 6. There Jesus also talks about remaining in him "Whoever eats my flesh and drinks my blood remains in me and I in him." (John 6:56).
The Church only grows by remaining united to Christ. As it does so, the Holy Spirit is free to grow the Church. We see this in the first reading from Acts as Barnabas introduces Paul to the Apostles. As they come to understand Paul's calling, they accept him, even risking their lives to rescue him. The Church was briefly at peace and the Holy Spirit caused the Church to grow.
Saint John also tells us in his epistle that "the way we know that he remains in us is from the Spirit he gave us." The peace we know as we remain in Christ comes from God who is greater than our hearts. Our hearts often condemn us for failing to keep his commandments. But because God is greater than our hearts, we can be confident that God will give us what we ask. John says that "those who keep his commandments remain in him."
We remain in Christ, the true vine by keeping his commandments. We gain strength to keep his commandments through the sanctifying grace of the sacraments. Through the forgiveness of sin in Confession, God prunes away the sins that injure, and even kill, his life in us. In the Eucharist, Jesus gives himself, his true life, to us. As we remain in his life, we will bear much fruit as his life grows in us. If we separate ourselves from Jesus, we will wither and die as a branch does cut off form the vine. Jesus himself says that without him we can do nothing. United to him, we will grow and bear fruit, glorifying the Father.