The central revelation of God’s character that Jesus makes during the Feast of Tabernacles shortly before his passion is the unique connection between God the Father, God the Son, and God the Spirit. Earlier in John 7, Jesus reiterated that his coming to this world was from “him who sent” him, who is the Father. Then, he explained that where he was going was inaccessible to the religious authorities. Finally, he declared that the purpose of his coming and going was to pour out his Spirit on those who would believe in him (John 7:37-39).
Thus, Jesus revealed the Fatherhood of God, his own Sonship, and the procession of the Holy Spirit into the very depths of believers. In short, Jesus revealed the triune character of God as he taught in amid the foggy notions of his ministry and message. And it is God’s character that helps us to make sense of both Jesus’ identity and his mission. That appears, to me at least, to be the point of John 7:25-52, but there is an interesting question worth taking up now regarding why the Holy Spirit would be given in the first place. It is to this question that the remainder of the reflection will turn.
Starting with a grammatical point, John’s gospel literally says in v39, “for the Spirit was not yet.” The ESV supplies “given” to complete the thought, though we could just as easily supply “poured out.” And perhaps “poured out” would make better sense given the “rivers of living water” metaphor in v38. Beyond that, any attentive Bible reader knows that the Holy Spirit had already been given, e.g. to Samson, Saul, and David. This suggests what we, living on the later side of Pentecost, know to be true: after his ascension, Christ poured forth his Spirit upon those who believed in his name.
But why does Christ prophecy the future pouring forth of the Spirit here? There are many reasons, including that the Spirit is a witness of our adoption as sons of God and that the Spirit is our divine prayer partner, for “the Spirit himself intercedes for us with groanings too deep for words” (Rom 8:26 ESV). One major reason for the Spirit, though, is that he came to lead God’s people into all knowledge.
Because my final application is focused on developing a deeply rooted discipleship in the knowledge of God, it’s worth thinking for a minute how the Spirit enables us to know God. Sinclair Ferguson draws out some implications of the Spirit’s teaching ministry:
When the Spirit comes he … brings illumination to Christ's disciples. By the Spirit they will be taught inwardly the nature of their relationship to Christ as well as Christ's relationship to the Father; “on that day you will realize that I am in my Father, and you are in me, and I am in you” (Jn. 14:20). “That day” in this context looks forward not only to Christ's resurrection but also to the gift of the Spirit at Pentecost. … The Spirit would help the disciples to grasp the intimacy of the Son's indwelling by and of the Father—what earlier theologians called circumincessio or perichoresis, the mutual indwelling of one another by the persons of the Trinity, the “dancing around” of each other in which the mutual harmony and love among the persons of the Trinity find expression. … Even more than this is taught by the Spirit. From him the disciples learned that they are “in” Christ and Christ also dwells in them. Rather than “losing” him, they will “gain” him in a more intimate way.
Ferguson hits on my final application in that one of the primary teaching topics for the Spirit is God’s triune essence. He doesn’t do this teaching without an instrument, however. The Spirit is our divine reading partner, leading us into all truth as we engage with the Scriptures of the Old and New Testaments.
One important implication of this is that we come to understand God best and mostly clearly as he has revealed himself precisely because he himself teaches us. Otherwise, while we might have moments of clarity, we remain in the fog like Jesus’ conversation partners in John 7 without the pouring out of the Spirit. This is all the more reason, then, to aim for a deep discipleship, since you have the Spirit who gives you access even to the mind of Christ.
 Sinclair B. Ferguson, The Holy Spirit, Contours of Christian Theology (Downers Grove: InterVarsity Press, 1996), 187–88.  Unbelievers can get something right about who God is, for God’s common grace can extend to deep insights from the Scriptures by those who don’t believe that Jesus is Lord (cf. Joel R. Beeke and Paul M. Smalley, Reformed Systematic Theology (Wheaton, Illinois: Crossway, 2019), 3.89-91). What unbelievers can’t get right is the saving significance of those insights.