John 14:15 “If you love me, keep my commands. 16 And I will ask the Father, and he will give you another advocate to help you and be with you forever— 17 the Spirit of truth. The world cannot accept him, because it neither sees him nor knows him. But you know him, for he lives with you and will be in you. 18 I will not leave you as orphans; I will come to you. 19 Before long, the world will not see me anymore, but you will see me. Because I live, you also will live. 20 On that day you will realize that I am in my Father, and you are in me, and I am in you. 21 Whoever has my commands and keeps them is the one who loves me. The one who loves me will be loved by my Father, and I too will love them and show myself to them.”
Who is the Holy Spirit? Jesus refers to the Spirit as ἄλλον παράκλητον: he is ‘another paraclete in his likeness’. Jesus introduces the Spirit by describing what he will do. Just as Jesus has advocated for, encouraged, comforted and enabled the disciples, so will the Spirit. This is the role of a paraclete.
As to his nature, a fundamental characteristic of the Spirit is Truth (John 15:26; 16:13; 1 John 4:6; 5:6). He reveals the truth, gives discernment of the truth and enables us to walk in the truth.
And he is God with us and in us. Just as the Father indwells the Son (John 14:10), so the Spirit will in dwell the Christian. Instead of Jesus leaving his disciples without protection, without encouragement or support, Jesus comes to them in the person of the Spirit.
Pondering this reality, John Calvin wrote, “so long as we are without Christ and separated from him, nothing which he suffered and did for the salvation of the human race is of the least benefit to us. To communicate to us the blessings which he received from the Father, he must become ours and dwell in us… The whole comes to this that the Holy Spirit is the bond by which Christ effectually binds us to himself.” (Institutes Book III.1)
Therefore, lest we view the Spirit as an ‘optional extra’, in verse 19 we learn that the life of the Christian is entirely dependent on the resurrection life of Jesus. We only live because he lives, effected by the Holy Spirit. In the same way that the Father is in the Son; so now, by the Spirit, the Son lives in us. The mystery of the Trinity is enlarged to embrace our lives, too. Amazing!
ALMIGHTYGOD, who as at this time didst teach the hearts of thy faithful people, by the sending to them the light of thy Holy Spirit; Grant us by the same Spirit to have a right judgement in all things, and evermore to rejoice in his holy comfort; through the merits of Christ Jesus our Saviour, who liveth and reigneth with thee, in the unity of the same Spirit, one God, world without end. Amen. (BCP, Whitsunday)