What does John 15:5 mean?
Among Jesus' more famous analogies is that of the vine and branches. In this passage, Jesus has compared the abundant life He offers (John 10:10) to that relationship. Some branches are "in the vine," only in the sense that they're intertwined or touching the other branches. Yet, they are not truly part of the life of the plant. In this context, these are the people Jesus refers to as "in me" but barren (John 15:2). Those "branches" merely associate with Christian faith, identify with believers, or attend a church. But only branches truly connected to the source of life will produce fruit—just as only truly born-again Christians will produce spiritual fruit (John 15:4).This is the end of a progression which began in verse 2. The process of growing from spiritual barrenness, to spiritual productivity, to spiritual abundance, is possible only through Christ. In the context of this analogy, Jesus distinguishes between branches which are "in" the vine from those which truly "abide in" the vine. The discarded branches Christ speaks about here are those who were never saved in the first place. True salvation cannot be lost, but those who have only an appearance of faith will be judged accordingly (Matthew 7:21–23).
Verses 1 and 5 of this chapter are the seventh of seven times (John 6:35; 8:12; 10:7–9, 11; 11:25; 14:6) where Jesus uses this specific "I Am" terminology in the gospel of John. This echoes the way God identified Himself to Moses from the burning bush (Exodus 3:14).