From Why We Pray by William Philip, as featured at Truth For Life:
How do we know Abraham had faith? Well, Hebrews 11:8 is plain. We know he had faith because he obeyed God when God called him. When God spoke to him and told him to go out to a place that he never knew, he responded and obeyed: “By faith Abraham obeyed when he was called.” We might say that Abraham’s obedience was the visible form of his faith. But the audible form of his faith, of his real and living relationship with God, was that he talked with God. God spoke to Abraham that word of great promise, and Abraham responded. “Abraham called upon the name of the Lord” (Gen. 12:8). In other words, Abraham prayed.
Prayer was the audible form of Abraham’s faith, as it is of all faith. Speaking to God in prayer is simply the audible response to God’s call to us, just as following him in obedience is the visible response to the call that marks out real faith and is the evidence of a real and living knowledge of God. Prayer is responding to God’s gracious word of salvation in his wonderful promise of his saving gospel. And if Hebrews 1 tells us that God spoke his ultimate word in the person of his Son, the Lord Jesus Christ, then that means fundamentally that prayer is simply responding in faith to the Lord Jesus Christ.
Prayer is answering God’s call to human beings in Jesus, answering it with all that we are and all that we have, not just with our lips but with our lives, so that our words, in that sense, are simply vocalizing what’s on the inside. It’s the inside reality coming out in an audible form. I remember my father explaining it to me this way: “It’s not so much what we pray but what we are when we pray that matters.” That’s true, because real prayer is anything that comes from a heart truly responding to the Lord Jesus Christ. It is the multitude of responses that come from a life that has found Christ.
Why We Pray, William Philip, Crossway, 2015.