What is the central point about prayer in the parable of the unjust judge?

And the Lord said, "Hear what the unrighteous judge says. 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 speedily. Nevertheless, when the Son of Man comes, will he find faith on earth?" (Luke 18:6-8)

Jesus told two parables to his disciples regarding the nature of how they should pray:  

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• First, Jesus told a parable regarding an unjust judge who eventually granted a widow's request so she would leave him alone to promote persistence in prayer. However, it is crucial to note that Jesus is not condoning a full import of the parable, whereas God has attributes similar to that of the unjust judge, for God is not an unjust judge just as “God is not a reluctant friend (Luke 11:5-8)” (Howell, 257). “Instead, it draws a contrast between God and the judge” (Elwell, 830) by answering two theological questions: “Will God vindicate his people?” and “Will they have to wait a long time?” Jesus' parable demonstrates that since God is not like the unjust judge that yes, God will answer persistent prayer “even more certainly than the unjust judge who eventually acted contrary to his character” and that yes God will grant justice quickly for again, He “is not like the judge who had to be pestered before he gave in to the widow” (Marshall, 676). Jesus question in 18:8 must have raised a host of questions for his disciples as it does for modern commentators. Since the question is clearly couched in eschatological imagery, Marshall sees that “the question as a whole presupposes a time of tribulation for the disciples in which they may be tempted to give up faith because their prayers are not answered” (Marshal, 676). However, whether Jesus had the 12 disciples in mind, or subsequent generations of disciples who might cease in their persistence from apathy or give up because” vindication will not seem to be quick at all for people on earth, but will be agonizingly slow...” (Elwell, 830), cannot be determined. Regardless, Jesus is telling the 12 and modern disciples “to be bold and persistent in bringing their requests to God” no matter the context (Howell, 257).
  
  
• Second, Jesus told a parable regarding a Pharisee who prayed a self-righteous prayer and a sinner who prayed a penitent prayer to promote the correct Heart attitude in prayer. Just like the Sermon on the Mount, “...Jesus' lesson is precisely that the attitude of the heart is ultimately what matters, and justification depends on the mercy of God's favour...” (Marshall, 681), not on the works we do for God (such as fasting & giving).
  

• Marshall, Howard I.. Gasque, W. Ward. The New International Greek Testament Commentary: The Gospel of Luke. Grand Rapids: William B. Eerdmans Publishing Company. 1978.
  
• Elwell, Walter. A.. Evangelical Commentary on the Bible. Grand Rapids: Baker Book House. 1989.
  
• Howell Jr., Don N.. The Passion of the Servant. Eugene: Wipf & Stock - Resource Publications. 2009.