1 Chronicles 14:10 NKJV - "And David inquired of God, saying, 'Shall I go up against the Philistines?'...The Lord said, 'Go up, for I will deliver them into your hand.'"
You may have to read the context of both these passages but I want you to note the difference in how God answered each prayer from two different kings. The statement in 2 Chr. 20:15 was directed to King Jehoshaphat where God told Jehoshaphat that he would not have to fight the battle, God would take care of it and deliver him from his enemies. The 1 Chr. 15:10 passage is when David faced the Philistines and God told him basically to "go out and fight" and God would give him deliverance. In one instance, the believer didn't have to fight; in the other instance, the believer was called on to fight and find the deliverance in the battle.
When we pray we all too often want God to answer our prayers without much effort from us. That really is very unrealistic praying! Not only is praying "hard work" but sometimes God calls us to be the answer to our own prayers. The next time you pray "for the Lord of the harvest to send laborers into His harvest fields," you might find His answer when He sends you!
In our prayers we give God our requests. In God's response He sometimes leads us to be part of His answer.