John 20:21-23 spotlights two aspects of the disciples’ mission in the Gospel. First, their mission is grounded in the character of the triune God. All three members of the Trinity are active in the church’s mission. Likewise in the midst of his final discourse to his disciples, Jesus promises that he will send the Holy Spirit, the Paraclete, from the Father in order to join with believers in witnessing on behalf of Jesus (Jn 15:26-27; cf. Jn 14:26). In John, God’s love moves to send the Son and Spirit for the world’s salvation and Jesus’ followers are caught up in that same current of love. The church participates in the mission of the triune God.
Second, the disciples’ mission is defined in the first place by their relationship to Jesus, rather than what they do or say. John does not narrate stories of Jesus sending the disciples out to preach and heal on their own (cf. Mt 10:1-42; Mk 6:1-6; Lk 9:1-6; 10:1-20). Their mission only has meaning because they are in relationship with Jesus and are part of his sending. As Andreas J. Kostenberger observes, “the disciples are not just to represent Jesus… the are to re-present him, i.e., Jesus will be present in and through them in his spirit as they fulfil their mission in the world.” in John 17, Jesus prays that just as there is a mutual indwelling between the Father and the Son, so Christians might live “in us”. The result of this sharing in the life of the triune God is “that the world may believe that you have sent me” (Jn 17:21). The relationship spawns the mission….
… As a result, John’s understanding of mission frees us from having to place our priorities on activities and accomplishments. As a missionary and an “achieving” personality, I know the pressure of feeling I have to justify my ministry through what I am doing for God and his mission. Not just the world, but too often the church tends to measure success by activity, effort and performance. For many sincere Christians, “doing” becomes the focus. This is precisely why we need to hear John’s accent on “being”. He reminds us that the only way that we can produce lasting fruit is to be intimately connected to the vine, Jesus Christ (Jn 15:1-16). This is not an excuse for inactivity. But mission flows from our relationship with God, not what we do for God. (Emphasis mine.)
From Recovering the Full Mission of God by Dean Flemming p.121 & p.129.