Holiness, unity and joy
Jesus knows that his return to the Father (11,13) will result in the disciples being in the world without the protection of his presence (12). But he will not leave them as orphans – by his Spirit he’ll be with them (14:17-18) and God the “holy Father” will protect them. This title is uniquely used here. It combines both awesomeness and intimacy, and leads on to his prayer that both he and the disciples will be sanctified (made holy, consecrated). Both Jesus’s holiness and ours are bound up with the holiness of God (1 Pet.1:16).
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The Father will protect them by the same means that Jesus had used i.e. by the power of God’s name (11-12). God’s name refers to the whole nature of God which Jesus had revealed to them (6). So he prays that God will keep his disciples faithful to that revelation. He prays this for a specific reason, “that they may be one as we are one” (11; 21-23).
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The only way we can share the unity which Jesus has with the Father is through the revelation of God in Jesus. God’s own holy and gracious character is the basis of our unity. And of our joy. It’s by remaining in Jesus and in the Father that our joy will be complete (15:11) and here again he promises his own joy within us (13).