"I am the true vine, and my Father is the vinegrower. He removes every branch in me that bears no fruit. Every branch that bears fruit he prunes to make it bear more fruit. You have already been cleansed by the word that I have spoken to you."
Uncle Dennis is a farmer. He has an orchard of all kinds of fruit trees on the Big Island. He took me through it a while back. He introduced me to fruit I'd never even heard of (loquats?!?) and told me his secret for his "sweetest tangerines in Hilo" moniker: pruning! "I prune off more tangerines in my orchard than most people have on their trees!" He said he likes to keep his fruit on the "outside" of the trees - where each can be facing the direct sunlight at some point during the day. His pruning techniques work amazingly well, too! (Though I admit it was strange to see potential fruit "wasted." He reminded me it's not wasting, but pruning in order to maximize the harvest quality!)
Jesus uses the same imagery to talk about our relationship with God - but with grapes & vines, not tangerines & trees! Branches that don't bear fruit get cut off... branches WITH FRUIT get pruned in order to "maximize the harvest quality." How does God "prune" us? Through life circumstances? Sometimes. Through relationships with others? Of course. But the word Jesus uses for "prune" in verse 3 has the same root for the word "cleansing," which is also used later in that sentence. So were pruned/cleansed by "the word that I have spoken to you." Jesus' words. Jesus' instructions. His stories, parables, teachings, actions & endeavors from the Gospels should be our "pruning shears." Things in our lives that are generally going well (fruit) need to be pruned by Jesus' life & teachings, so we can be even better!
But don't just take my (and Jesus') word for it... Uncle Dennis will back us up, too!