The same lesson is taught in a very striking way in the second passage in Luke to which I have already referred, Luke 18:1-8: “And He spake a parable unto them to the end that they ought always to pray, and not to faint; saying, There was in a city a judge, who feared not God, and regarded not man: and there was a widow in that city; and she came oft unto him, saying, Avenge me of mine adversary. And he would not for a while: but afterward he said within himself, Though I fear not God, nor regard man; yet because this widow troubleth me, I will avenge her, lest she wear me out by her continual coming. And the Lord said, Hear what the unrighteous judge saith. And shall not God avenge His elect, that cry to Him day and night, and yet He is long-suffering over them? I say unto you, that He will avenge them speedily. Nevertheless, when the Son of man cometh, shall he find faith [literally, ‘the faith’] on the earth?”
What the central lesson in this parable is, we find in the words with which our Lord Jesus opens the parable, which are really the text of the whole parable; these words are, “Men ought always to pray, and not to faint,” the clear meaning of which is, that when we begin to pray we ought to pray on and on until we get the thing that we desire of God.
The exact force of the parable is, that if even an unrighteous judge will yield to persistent prayer and grant the thing that he did not wish to grunt, how much more will a loving God yield to the persistent cries of His children and give the things that He longs to give all the time, but which it would not be wise to give, would not be for the person’s own good to give, unless they were trained to that persevering faith that will not take “no” for an answer. So we see again that God does not always give us at the first asking what we desire of Him in prayer. – R. A. Torrey
Excerpt from Praying Through “Power of Prayer and the Prayer of Power”