John 15 marks a transition in Jesus’ farewell discourse from the prior focus on how the disciples might let faith triumph over fear to a discussion of what comes next after faith is firmly established. Where there is a transition, it is more of an expansion of his teaching on the powerful presence of the promised Holy Spirit. As I mentioned last week, the physical absence of Christ does not mark his complete absence but a transition to his abiding spiritual presence through the indwelling Holy Spirit. The Father and the Son take residence, as it were, in believers through the Holy Spirit.
And it is this connection between the indwelling Holy Spirit and the spiritual presence of Christ that now gets developed in the first part of John 15. Using the imagery of vines and branches, which would have been a common figure for the day, Jesus teaches his disciples that the ground for their fruitfulness is their vital connection to him. Just as a branch has no life apart from the vine, so no follower of Christ has life apart from Christ. This idea is what theologians call union with Christ, and it is closely tied with the presence of the Holy Spirit.
But before the Holy Spirit unites anyone with Christ, he must first bring about the new birth. The reality is that the union is with believers, i.e. those who have professed the true religion. Subjectively or existentially speaking, before conversion, everybody is a dead branch, severed from the life-giving vine and unable to do anything. Thus, Jesus says in our text, “I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing” (John 15:5 ESV). Just as this is true on an on-going basis, it is also true prior to conversion.
Picking up on the interplay between bearing much fruit and doing nothing, Herman Ridderbos suggests that the key idea in this verse is not inactivity but “total unfruitfulness.” For this reason, he says that this total unfruitfulness can also manifest as “lapsing into the [kind of] wild growth that is no longer shaped by [Christ’s] word, into activism or idealism that is neither derived from nor directed to him.” This is a kind of growth for growth’s sake that never actually ends up producing any fruit. It is a wild shoot that does nothing in the sense that it does not bear much fruit.
And this idea of a wild and fruitless shoot brings to mind Paul’s use of similar imagery in Romans 11. There, Paul describes the Gentile converts as wild olive shoots that were grafted onto the cultivated olive tree (cf. v17). There is a taming effect, then, of the Spirit’s work in both regeneration and union in Christ. As the wild, fruitless shoots are plucked up and grafted onto the cultivated vine, what was once a very active “total unfruitfulness” now issues in a generous yield of fruitfulness. To be sure, the ground of our fruitfulness is union with Christ, but so also the consequence of our union in Christ is fruitfulness.
Turning to an application of these thoughts, the act of being united to Christ also “confers a new and noble identity” upon the wild shoots who are engrafted into the cultivated, true vine. Upstream of any fruitfulness is the fact that what we are called does actually make a difference. In the first place, it means that we have great dignity, for we are now given the family name of God as we are called Christians. More than that, we have great reason to be confident in prayer because our new name gives us access to the Father. Furthermore, we have every reason to be strong in temptation because our identity is not merely some paper credential but a vital union with our elder brother Jesus, who provides what we need to glorify the Father with him. And finally, all of this means that we have a compelling reason to speak and act differently than the rest of the world. As we are tamed wild shoots, so we are called to live that cultivated life in full union with Christ and communion with the Father.
 Herman N. Ridderbos, The Gospel According to John: A Theological Commentary, trans. John Vriend, Eerdmans Classic Biblical Commentaries (Grand Rapids: Eerdmans, 2018), 517.  Joel R. Beeke and Paul M. Smalley, Reformed Systematic Theology (Wheaton, Illinois: Crossway, 2019), 3:263.  These three applications are found in Beeke and Smalley, Reformed Systematic Theology, 3:263.