As Bill Hybel writes in Too Busy not to Pray, "We pray because, by intuition or experience, we understand that the  most intimate communion with God comes only through prayer. Through prayer God gives us his peace, and that is one reason  even self- sufficient people fall  on their knees and pour out their hearts to him. 

But there is another reason.

People are drawn to prayer because they know that God’s power flows primarily to people who pray. If you are willing to invite God to involve himself in your daily challenges,  you will experience his prevailing power- in your home, in your relationships, in the marketplace, in the schools, in the church, wherever it is most needed.

That power may come in the form of wisdom- an idea you desperately need and can’t come up with yourself.  It may come in the form of courage greater than you could even muster. It may come in the form of confidence or perseverance, uncommon staying power, a changed attitude toward a spouse or a child or a parent, changed circumstances, maybe even outright miracles.  However it comes, God’s prevailing power is released in the lives of people who pray."