NOTES for Jud 1:20-21
Describing the spiritual life of the Christian, Jude speaks about faithfulness ("faith"), with which Christians are built or organize themselves, praying in the Holy Ghost, keeping themselves in the love of God and waiting for the favor or the mercy (the Greek corresponding word supposes both meanings) of Jesus Christ, which is necessary for them for to have the eternal life (it is obviously about the life of the Kingdom in all its fullness). As we see, the apostle understands perfectly that the current situation of the Christians cannot yet be considered definitive, that their definitive communion with the Kingdom and its life in all its fullness, and it is connected to the mercy manifested in Jesus Christ. There is nothing surprising in such a look: because the spiritual fate of every Christian is connected to the fate of the Kingdom, to the life with which he is implied. And it is impossible to receive the Kingdom, to communion with it by merit: man cannot deserve by definition the Kingdom.
And that is why Jude speaks about the mercy: because since in the days of Hosea the notion of God's mercy was connected to God's will to make for man or for His people more than this man or these people deserves. Only so the fallen man receives the possibility of entering the Kingdom, of joining the fullness of its life. But Christians can not join the fullness of the Kingdom earlier, than this fullness will reveal itself in the world and for the world, by transforming it and by renewing. And as long as this did not occur, Christians are called to live the life of the Kingdom in this measure, in which it is revealed to them at a given concrete moment. That is why the apostle speaks about faith and about prayer in the holy Spirit: it is about what without which the communion with the Kingdom is in principle impossible.
The Kingdom is totally penetrated by the breath of God, and its basis is formed by these relationships that bind believers to Christ and to one another. Keep the faithfulness to the One, Who brought the Kingdom into the world and to breathe its breath - that's it the basis of a Christian spiritual life. And of course love, this same love, that Jesus spoke about at the Last Supper, the love manifesting already not simply relations, as it was before, but become the spiritual nature, a kind of substance of the Kingdom. It is in particular its action that changes man, by transforming his nature, preparing him for the moment, when he can, the day of the return of the Savior and the triumph of the Kingdom, join the new life in all his fullness.