“In John's narrative, neither death nor door locks prevent Jesus from commissioning his followers. After proclaiming peace and proving he has conquered death, Jesus utters these astounding words: ‘As the Father has sent me, I am sending you’ (20:21).
This scene is John's version of the Great Commission. It helps us understand both the apostolic nature of the church and also the nature of God.
Both the noun apostle and the adjective apostolic derive from the Greek verb apostello, meaning ‘to send.’ The Latin equivalent is missio, from which we get the English word mission. Therefore, the apostolic church is a missionary church; it seeks to faithfully take Christ's mission into the world. True apostolicity is not so much a matter of succession of leadership or transmission of a message as it is obedience to God's mission. And if the church's mission is to be useful, the church's leadership needs to model the apostolic gospel.
But Jesus doesn't send the apostles out on their own mission; he connects their mission with the very activity of the triune God: The Father sends Jesus into the world, and Jesus sends the church in the power of the Holy Spirit.
Mission begins not with the church but with God himself. This idea is known as Missio Dei, which literally means ‘the mission of God.’ German theologian Jürgen Moltmann captured it well: ‘It is not the church that has a mission ... it is the mission of the Son and the Spirit through the Father that includes the church.’ South African missiologist David Bosch similarly said, ‘Mission is not primarily an activity of the church, but an attribute of God. God is a missionary God.’ This is why we should speak of ‘mission’ rather than ‘missions,’ because the church is caught up in the singular mission of the triune God.”
— Krish Kandiah, An Explosion of Joy