The reason for this parable was clearly stated in verse 1: ( for us to pray always). However, it'll be great if we know what we ought to pray for. Now let's read Luke 18:1-7 (KJV)
1:And he spake a parable unto them to this end, that men ought always to pray, and not to faint;
2:Saying, There was in a city a judge, which feared not God, neither regarded man:
3:And there was a widow in that city; and she came unto him, saying, Avenge me of mine adversary.
4:And he would not for a while: but afterward he said within himself, Though I fear not God, nor regard man;
5:Yet because this widow troubleth me, I will avenge her, lest by her continual coming she weary me.
6:And the Lord said, Hear what the unjust judge saith.
7:And shall not God avenge his own elect, which cry day and night unto him, though he bear long with them?
From the passage, we see the widow was praying for what she rightfully deserved from the judge; justice (the GNB recorded that "she was pleading FOR HER RIGHTS"). This is synonymous to praying not just for what we desire, but what we deserve according to God's will for our lives. Because the woman was right in her request, the judge was troubled and not loath to grant her justice.
If only we knew the long term effects of some of our prayer requests, we wouldn't ask for them anymore. However, because of our persistence, God may reluctantly answer those prayers and we eventually regret it.
