Why unity is essential
This verse brings to a head much of what Jesus has prayed in the previous two verses (21-22). He longs for his people to have the same unity together which he himself has with the Father, and he affirms again that it is our being in him which makes this possible: “I in them and you (Father) in me”. This echoes his repeated emphasis to them that evening, in which the ‘how’ of fruitfulness depends on being in Jesus just as Jesus is in the Father (14:20; 15:9-10).
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So he longs for us “to be brought to complete unity”. This is essential if we are to be effective in continuing Jesus’s work in the world. Only when we demonstrate a unity which is rooted in the Father and the Son will the world be able to believe that Jesus was sent by God (21) and believe too that God loves each one of us just as much as he loves his own Son (23).
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In Christ we have a spiritual unity which transcends all barriers of race, culture and denomination (10:16; Gal.3:28). But human nature is a constant threat to that unity (Acts 6:1; 1 Cor.1:12) and so we must “make every effort to keep the unity of the Spirit” (Eph.4:3). In all our relationships, both within each church and between churches, love is the key to doing that (13:34-35).