The Bible shows many examples of the effectiveness of persistence in prayer. We have included a couple below.
Luke 18:1-7 (New International Version)
The Parable of the Persistent Widow
Then Jesus told his disciples a parable to show them that they should always pray and not give up.
He said: “In a certain town there was a judge who neither feared God nor cared about men. And there was a widow in that town who kept coming to him with the plea, ‘Grant me justice against my adversary.’
“For some time he refused. But finally he said to himself, ‘Even though I don’t fear God or care about men, yet because this widow keeps bothering me, I will see that she gets justice, so that she won’t eventually wear me out with her coming!’ ”
And the Lord said, “Listen to what the unjust judge says. And 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… ” (emphasis added)
Daniel 6:6-23 (New International Version)
Daniel in the Den of Lions
So the administrators and the satraps went as a group to the king and said: “O King Darius, live forever! The royal administrators, prefects, satraps, advisers and governors have all agreed that the king should issue an edict and enforce the decree that anyone who prays to any god or man during the next thirty days, except to you, O king, shall be thrown into the lions’ den. Now, O king, issue the decree and put it in writing so that it cannot be altered—in accordance with the laws of the Medes and Persians, which cannot be repealed.” So King Darius put the decree in writing.
Now when Daniel learned that the decree had been published, he went home to his upstairs room where the windows opened toward Jerusalem. Three times a day he got down on his knees and prayed, giving thanks to his God, just as he had done before.
Then these men went as a group and found Daniel praying and asking God for help. So they went to the king and spoke to him about his royal decree: “Did you not publish a decree that during the next thirty days anyone who prays to any god or man except to you, O king, would be thrown into the lions’ den?”
The king answered, “The decree stands—in accordance with the laws of the Medes and Persians, which cannot be repealed.” Then they said to the king, “Daniel, who is one of the exiles from Judah, pays no attention to you, O king, or to the decree you put in writing. He still prays three times a day.”
When the king heard this, he was greatly distressed; he was determined to rescue Daniel and made every effort until sundown to save him. Then the men went as a group to the king and said to him, “Remember, O king, that according to the law of the Medes and Persians no decree or edict that the king issues can be changed.” So the king gave the order, and they brought Daniel and threw him into the lions’ den. The king said to Daniel, “May your God, whom you serve continually, rescue you!”
A stone was brought and placed over the mouth of the den, and the king sealed it with his own signet ring and with the rings of his nobles, so that Daniel’s situation might not be changed. Then the king returned to his palace and spent the night without eating and without any entertainment being brought to him. And he could not sleep.
At the first light of dawn, the king got up and hurried to the lions’ den. When he came near the den, he called to Daniel in an anguished voice, “Daniel, servant of the living God, has your God, whom you serve continually, been able to rescue you from the lions?”
Daniel answered, “O king, live forever! My God sent his angel, and he shut the mouths of the lions. They have not hurt me, because I was found innocent in his sight. Nor have I ever done any wrong before you, O king.” The king was overjoyed and gave orders to lift Daniel out of the den. And when Daniel was lifted from the den, no wound was found on him, because he had trusted in his God.