When we speak the word of God in prayers, we are expressing our belief that God exists. Otherwise, it would make no sense to pray to a God who we didn't believe exists.
Further more, the reason we are certain that God will respond favorably to our prayers comes not from human knowledge, but from knowledge rooted in faith. Without such knowledge the physical person's belief in the existence of God could not endure for long.
Daily prayers reinforce our belief in God, and our sincerity when we say to Satan that we are parting company with him forever.
When you encounter difficulties finding the right words to pray, as sometimes happen, read the Psalm. The reach and depth of the prayers in the Psalm are able to capture our yearnings in ways that we are often unable to do in times of extreme pain, fear and uncertainty; and present them to God in our behalf.