“Then He said to me, ‘Do not fear, Daniel, for from the first day that you set your heart to understand, and to humble yourself before your God, your words were heard; and I have come because of your words. But the prince of the kingdom of Persia withstood me twenty-one days; and behold, Michael, one of the chief princes, came to help me, for I had been left alone there with the kings of Persia.”
Daniel 10:12-13 

Notice, the Lord heard Daniel’s prayer immediately. However, there was a spiritual battle taking place. It took twenty-one days for the angel to come back to Daniel with an answer. What if Daniel had stopped praying after the first day? What if he had stopped praying on the twentieth day? Daniel continued to pray for an answer. He didn’t stop. And, because of Daniel’s persistent prayers, the enemy was defeated!