Prayer is simply making your will and desires made to another. 
Often when it is made to another person, it is done to change their mind.
Most Christians carry this idea of prayer into their prayers to God. But God isn’t going to change His mind. For that matter, is God just a religious version of a genie, there to grant you wishes?
Throughout scripture, prayer to God is used most often to change the mind of the petitioner, not God. This is best illustrated by the prayers of the prophet Daniel, of Jesus Christ, and of the apostle Paul.