Jesus’ prayer in John 17:21, “that they may be one," the prayer of the departing Lord for the unity of his followers, has become one of the expressions of the ecumenical movement. The unity of believers in view in the Fourth Gospel is a unity based on the mutual indwelling of the Father and the Son on the one side and the believers on the other, and which is modelled on the union between the Father and the Son. But the unity also has a corporate component; to love one another as their Lord commands and live as members of one Vine and one Flock. The aim of this article is to investigate the idea of the unity of Christians in John’s Gospel whose goal is to inspire believers and motivate them to carry out their missions in the world.