God's people are "already" seated with him in the heavenly realms (Eph. 2:6) and blessed (Eph. 1:3), thus they are already royal subjects of his covenant Kingdom. While is is indeed an honor to be subjects of the Kingdom, Kingdom life in the "now, but not yet" is difficult and one should not give up. Rather God's subjects, his sons and daughters, should pray always. God is immanent. God listens to his people. He listens to prayer. He did not just windup the world and set it in motion and than remain removed from what was happening. Rather he is involved. So, involved that he sent his Son to literally die for his people. He is close. He is listening. He is concerned. He is present. He is working. He is ruling.
Paul says, "Since, then, you have been raised with Christ, set your hearts on things above, where Christ is seated at the right hand of God. Set your minds on things above, not on earthly things. For you died, and your life is now hidden with Christ in God. When Christ, who is your life, appears, then you also will appear with him in glory" (Col. 3:1-4; cf. Tit. 2:11-14). Once again, we see the "now" of the Kingdom ("you have been raised with Christ") and Paul says s focus on the "not yet" of the Kingdom ("Set your minds on things above" . . . "you also will appear with him in glory"). Christ initiated his Kingdom, it continues through his Church, and the consummation is still coming. God's Kingdom while already here (the "now" - initiated and continuing) is coming in its fulness (the "not yet" - its consummation). He will vindicate his people. "God bring about justice for his chosen ones, who cry out to him day and night?" (Luke 18:7).
With this brief introduction now we may begin to see the parable in the light it was meant to be seen in. Jesus sets the stage and introduces two main characters: (1) a judge, who does not fear God or care about men (Luke 18:2, 4) and (2) a persistent widow (Luke 18:3, 5). A widow was among the most vulnerable people in Jewish society. She was to be looked after by others (Deut. 10:18; 14:29; 16:11, 14; 24:17, 19-21; 26:1213; 27:19; Psa. 94:6; Is 1:17, 23; 10:2; Jer. 5:28; 7:6; 22:3; Ezek. 22:7; Mal. 3:5). In a civil dispute a judge would be responsible for dealing with the woman's claims. Since she is alone, if she is to find real justice, the judge must supply it.
What was Jesus teaching? Hughes says, "The parable of the unjust judge and the pestering widow is a parable of contrast. The clear lesson of the parable is that God is not like the judge, for God is good and gracious. And we are not like the nameless widow, for we are his chosen ones. So a distressed bugging of God is in fact inadequate prayer."
If an unjust judge looked after a widow, whom he saw as a mere pest, how much more shall the just Judge of the earth, lovingly care for his chosen people, who are full of faith. Continual prayer by God's people is not to pester God into submission to our wills (cf. 1 Kings 18:26-28) and should not be entered into with the attitude that if I may ring God's doorbell xxx number of times I can get what I desire from God. This - a prayer of idolatry - is not what the parable is teaching. It rather teaches that a true believer constantly prays because they have faith that their King is coming again to vindicate them. Jesus is coming again. As King he is also the Judge. His judgment at his coming shall be immediate.
In closing, Hughes comments on Luke 18:8 saying:
As we live in the not yet, longing for the return of the Son of Man, Jesus' closing question has the same force as it did in A.D. 33: "However, when the Son of Man comes, will he find faith on the earth?" (Luke 18:8). Jesus' question implies that such faith will not be found on earth unless his disciples learn to "always pray and not give up" (Luke 18:1).
Jesus was saying that continual prayer until he comes is not only the evidence of faith, but the means of building faith until his return. The God to whom we pray is not like the unjust judge who could only be badgered into responding, for our God is loving and gracious. And we are not like the nameless widow, for we are his chosen ones. Because of this, he delights to hear and quickly answer our prayers until he comes.
"When the Son of Man comes, will he find faith on the earth?" Yes, he will, if we have learned to live a life of prayer in the not yet.