From The Gospel of John, by Francis Martin and William Wright, commenting on John 14:25-29:
Throughout the Farewell Discourse, Jesus announces beforehand many things that will happen to the disciples (13:19; 14:29; 16:1, 4). Jesus has just told the disciples about the realities to be revealed at his resurrection, and he includes the future teaching activity of the holy Spirit. As the Father has sent Jesus, upon whom the Spirit descended (1:32–33), the Father will also send the Spirit in Jesus’ name and at his request (14:16). The Holy Spirit, who will dwell in Jesus’ disciples, will teach you everything and remind you of all that [I] told you.
There are several instances in the Gospel where disciples are said to remember episodes in Jesus’ ministry after his glorification (2:17, 22; 12:16). As this verse suggests, their remembering of Jesus’ ministry will be caused by the Spirit. It is not a simple recollection of the past but also a deeper understanding of Jesus and his work given by the Spirit—a spiritual understanding. The Spirit leads disciples into a greater understanding of the mystery of Jesus and makes it come alive for us.
Among his promises (14:18–24), Jesus includes the promise of his peace. Behind this mention of “peace” is the biblical promise of shalom (peace, wellbeing, everything is right), a blessing of reconciliation that God promised to bestow upon his people in his †eschatological act of salvation (Isa 52:7; 54:10–13; Jer 33:6–9; Zech 9:10). Jesus’ peace is a fruit of his relationship with the Father, into which he will bring his disciples. It is a supernatural peace that arises from a total love for the Father and therefore is unlike the peace of the world, which rejects God. Repeating his words of reassurance (14:1), Jesus calls the disciples to a confident, trusting faith and promises them the peace that comes from obeying the Father and knowing his love. We shall see this promise fulfilled in the Gospel account of Easter Sunday evening, when the risen Jesus gives the disciples his peace, which drives out their fear (20:19; see 20:26; 1 John 4:18). Paul similarly exhorts his readers, “Let the peace of Christ control your hearts” (Col 3:15).
Jesus continues to console his distressed disciples with the promise I will come back to you. He will return to them not only after his resurrection, not only at the †Parousia, but also during the present time through the Holy Spirit. While it may be very hard for them to grasp, the disciples should rejoice that Jesus is going to the Father. The Father is greater than Jesus in his mortal humanity, but at his resurrection and ascension, Jesus’ humanity will be glorified by the Father and become “greater” (see 14:12). Jesus’ entrance into heavenly glory opens up salvation and life with the Father, salvation and life for humanity (see Acts 2:33). Jesus has prophesied these things ahead of time, so that when they happen, the disciples may believe in him, believe that he is present to the Father and “has revealed him” (1:18).