Expositor's Bible Commentary Commentary John 17:21

"that they may all be one; even as thou, Father, [art] in me, and I in thee, that they also may be in us: that the world may believe that thou didst send me." — John 17:21 (ASV)

At this point, the burden of the prayer is for unity (cf. “one”; GK 1651). Jesus has already stressed the need for mutual love that will bind them together for their common task. Now, foreseeing the addition of many more who will increase the diversity of temperaments, backgrounds, and interests, he makes a special plea that all may be one. The standard is not an institutional but a personal unity.

Nor is he calling for uniformity, since he and the Father are distinct from each other and have different functions. He predicates that the unity will be one of nature; for he and the Father, while distinguishable in person, are one being. The new birth brings believers into the single family of God by spiritual generation (1:12–13; cf. 15:1–7; 1 Corinthians 12:12–13). The purpose of this unity is the maintenance of a convincing testimony before the world to the revelation of God in Christ and to his love for the disciples. Through the common witness and experience of the disciples, Jesus wishes to establish the fact of his divine origin and of the love of God for humankind.