Our God is verbal and He listens to us, so we should also be verbal and listen to Him. When we talk out loud it reminds us that the person we are talking to is near. When we pray out loud, we remember that God is right here with us—He is listening, He cares, and He will act. Powlison concludes,..."
http://www.christianheadlines.com/trending/how-praying-out-loud-is-helpful-to-spiritual-growth.html
-vk-