Jesus, the true vine
In the Old Testament Israel is said to be God’s vine (Psalm 80:8-16; Isaiah 5:1-7; Jer.2:21). But these passages all speak of Israel as a faithless vine that had failed to bear the expected fruit. It’s against that background that Jesus spoke his final “I am” saying, calling himself the true vine (1). It’s Jesus (not the church) which is the new Israel raised up by God to do his work. We are in him just as the branches are in the vine, and it’s his life in us, through his Spirit, which produces fruit.
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The fruit itself is not defined but it must refer to both of the themes which Jesus has been speaking about i.e. the future ministry of evangelism in his name (14:12; Rom.1:13; Col.1:6), together with the qualities of Christian living demonstrated especially by love and obedience (13:35; Gal.5:22; Eph.5:9).
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So, though Jesus warned of the seriousness of not bearing fruit (2), the point of the metaphor is to encourage his disciples that we can and will be fruitful, because the basis of that fruit-bearing is not our own human effort but our being in Jesus. The Father himself works to increase that fruitfulness in us, pruning our lives of dead wood so that we can be “even more fruitful”.