Jesus gives the Spirit a name: Paraclete. This name is variously translated Counselor, Comforter, or Advocate, and all of them apply. The term simply means one who is called to the side of another, to help, defend, protect, or otherwise “be there” for him. Christ Himself is the first Paraclete, who came to the side of sinful, exiled mankind as Savior and Redeemer. To make it clear that that’s how He thought of Himself, Jesus told the apostles that the Father would send another Paraclete (14:16), the Holy Spirit, to be with them. This Paraclete He called the Spirit of Truth (three times in the Farewell Discourse).
What will the Spirit of Truth do? Precisely as Spirit of Truth, He will “teach you all things and bring to your remembrance all that [Jesus has] said…” The Spirit will guide us into all the truth, speaking what the Father tells Him to, glorifying Christ by declaring to us his word. So the Holy Spirit is the life-breath of the living Tradition of the Church, leading her into the full truth about Christ and the Holy Trinity. The Spirit will safeguard the revelation, the heritage of Christ which He gave to his apostles, and will bring it to fresh vitality in every age and nation.
That is what the Spirit does for the Church. For the world: “He will convince [or convict] the world concerning sin and justice and condemnation.” The sin Jesus refers to is unbelief, the justice (or perhaps vindication) is his return to the Father after having completed his mission, and the condemnation is the judgment pronounced upon the devil (16:8-11). In terms of this passage the mission of the Spirit in the world is to call unbelievers to faith, to instruct them about the unique and absolute claims of Christ—based on who He is and what He has done for us—and to warn them of the condemnation that awaits those who would follow the evil one. Yet this task is difficult, for the world “neither sees Him nor knows Him.”
With the individual believer, the Spirit is more intimate. Once Jesus said the world doesn’t know the Holy Spirit, He said to his disciples: “but you know Him, for He dwells with you and will be in you.” That was just before Jesus said that He and his Father would come to us and make their home with us. So the Trinitarian indwelling is here completed. With us and in us—that is how God wants to be.
We have to rely heavily on the Spirit of Truth in this age of widespread deception. We so need to be reminded of all that Jesus said; we need to be led fully into the profound truth about God, the Church, the world, and even about ourselves. The Spirit is entirely Self-effacing, glorifying the Father and the Son; it is through the Spirit that the Father and the Son dwell in us and act in the world today. Pray to better recognize the Holy Spirit, to know Him, to love Him with that flaming intensity that only He Himself can inspire. The Spirit dwells with you and in you. Call to the Holy Spirit in your time of need. Let Him be the Paraclete in your life.