Jesus tells the parable of the widow and the unrighteous judge (Luke 18:1-6) in order to encourage us to pray - and not give up. He starts by tackling the idea the idea that our prayers have no impact: he talks about an unrighteous self-centred judge who answers petitions just to shut up a helpless widow so that she won't bug him any more - and then contrasts the unrighteous judge with the righteous judge of the world - God.
He then gives three encouragements to pray - and in so doing turns the whole question around:
“And will not God give justice to his elect, who cry to him day and night? Will he delay long over them? I tell you, he will give justice to them a speedily. Nevertheless, when the Son of Man comes, will he find faith on earth?” (Luke 18:7-8)
- The inductive: "And will not God give justice to his elect, who cry to him day and night? Will he delay long over them?" A rhetorical question - given all that you already know about God, why would you doubt that he'll answer?
- The explicit: "I tell you, he will give justice to them a speedily."
A strong affirmation that God isn't hanging around here - he's not busy and leaving you to go to answerphone - he's strongly committed to justice.
- The implicit: "Nevertheless, when the Son of Man comes, will he find faith on earth?"
Our knowledge of God leads us to be confident that he'll answer; the assurance of Jesus is that he'll answer so what's the real question? The real question is whether we'll pray.
Jesus' has turned the question on it's head: our real concern about prayer is shouldn't be about whether God will answer - but whether we'll even call. We can be confident that God will be faithful - but we can't assume that we will too.