Now He was telling them a parable to show that at all times they ought to pray and not to lose heart... Luke 18:1
Have you been praying for justice for a long time? Are you weary and tired of asking the Lord for what you need? Do you despair that God is not hearing you or that you have been put on "ignore?"
The Parable of the Persistent Widow (vv. 1-8) is told by Jesus to encourage us to continue to pray in the face of adversity. In the parable, the widow has been wronged, exploited if you will, and she wants justice! She has come before this same judge many times and has not gotten satisfaction.
The judge is not a righteous man and does not fear or honor God. He could care less about this widow and her problem, he just wants her to go away and leave him alone. He is tired of her coming before him and I can only suspect her agitation is growing with each appearance because the judge is fed up with her frequent tirades and is feeling really beat up by her incessant petitions ("wear me out" lit. hit me under the eye).
Eventually, the widow gets her way. She is vindicated! The wicked judge gives her justice if for no other reason than she has worn down his resistance.
Jesus uses this parable to encourage us to continue to pray for justice and vindication when we are wronged. He tells us that if the unrighteous judge was willing to give justice, our righteous God will do more.
...will not God bring about justice for his chosen ones, who cry out to him day and night? Will he keep putting them off? I tell you, he will see that they get justice, and quickly. Luke 18:7-8 (NIV)
The Lord wants us to continue to pray and not to lose heart while we are waiting for justice. A time is coming when the Lord will bring all things to a conclusion. Until that time Christians are going to suffer at the hands of unjust and ungodly people. The Word of God and our belief in God will continue to be attacked and made fun of. The Lord Jesus Christ will be demeaned and insulted and mocked and those to believe in Him will also suffer those slings and arrows.
Until Christ comes again we are to wait and pray. We must not lose heart, even when it looks hopeless.