"To more strongly impress the truth that men ought always to pray, and not to faint (Luke 18:1) and that if their prayer is not soon heard, that they should continue to pray, the Lord told a parable about the judge who did not fear God and neither regarded man. The judge complied at last with the widow’s petition, not because he feared God and regarded man, but only because that widow would not give him peace. So, if such a callous man could not withstand the persistence of this woman’s petition, will not God, who loves mankind and is filled with mercy, fulfill a petition raised up to Him persistently, with tears and contrition?! Here is the answer to why our prayers are often not heard: Because we do not send up our petitions to God zealously, but as though in passing; furthermore, we pray once today, then expect our prayer to be answered by tomorrow, not thinking to sweat and trouble ourselves any more in prayer. That is why our prayer is neither heard nor answered. We ourselves do not fulfill as we ought the law laid down for prayer—the law of hope-filled and zealous persistence."
-St. Theophan the Recluse