In this passage, Christ is offering us a remedy for the poison of arrogance, which is overestimating your own holiness. Jesus says this so none of us will think that our own suffering, apart from Christ, can attain forgiveness of sins or make us fruitful branches in the sight of God. Here's what usually happens: Someone does many good works and endures much suffering. That person becomes aware of producing fruit. In other words, they are aware of achieving something through preaching or some other method. Then that sweet poison begins to make the person think, "Oh, I have now done something that will make God notice me and be merciful to me." In this way, little wild branches begin growing alongside the true branches. These wild branches steal the sap and energy from the true branches so that they don't flourish. That is why the Gardener must be alert. He has to restrain such arrogance and presumption by constant application of the Word.
Christ is saying here, "You aren't clean because of what you do, what you suffer, or the fruit you produce. You wouldn't have done any of these things if you hadn't already been pruned and been made into good and true branches. Only God's Word can make you clean." It must be present at all times. The Father sends various kinds of suffering, danger, anxiety, need, and temptation to you so that you may hang on to God's Word tightly and so that it may work powerfully in you. In this way, he humbles you and teaches you that you can't make yourself clean. Your suffering doesn't make you clean before God. Yet it drives you to reach for God's Word and hold on to it more tightly and firmly. This is how God exercises your faith.
Grace, Freedom, Laughter!