The clearest hints of this identification of ministries [the Holy Spirit as the Spirit of Christ] are found in John’s Gospel, particularly in the farewell discourse. There, however, the identification is underlined to assure the disciples that the ministry of the Spirit stands in total continuity with that of the Son. Like Jesus, the Paraclete is sent by the Father and comes from the Father. Jesus is the truth, the Paraclete is the Spirit of truth who leads Christians into the truth (Jn. 14:6, 17; 15:26; 16:130; Jesus is the teacher of his disciples (14:23, 26); the Paraclete comes to teach them further. Jesus is the witness God has sent; the Paraclete is sent into the world to be a witness (18:37; 15:26). The world does not know or accept Jesus (5:43; 12:48); nor does the world recognize the Paraclete (14:17). In all of these senses the Paraclete is the one who ‘takes what belongs to Jesus’ (cf. 16:14).

Thus, when Jesus announces his departure from the disciples but assures them that ‘I will come [back] to you’ (14:18), he is speaking neither about his resurrection reappearance (20:14, 19), nor about his anticipated final return, but about his ‘coming’ in the gift of the Spirit. So complete is the union between Jesus and the Paraclete that the coming of the latter is the coming of Jesus himself in the Spirit. . . .

The ministry of the Spirit in this increasing identification with Jesus is in order that, being ‘shaped’ as messianic Spirit by the life and ministry of Jesus, he may come to us thus qualified to reshape us to be ‘like Christ’, from one degree of glory to another (2 Cor. 3:17-18). This is the central function of the Holy Spirit in the life of the Christian believer.[1]

[1] Sinclair B Ferguson, The Holy Spirit, Contours of Christian Theology (Downers Grove, IL: InterVarsity Press, 1996), 56.