What is kavvanah, anyway? Why do we need it?
Tefillah is hard to do right. It is difficult when you do not know the language or the melodies, but it is even more difficult, arguably, when you know it so well that it becomes rote. So we all need a focal point, something that helps us make the tefillah meaningful and valuable. Kavvanah, literally "intention" or "direction," can be that focal point.
Here is something from the Mishnah, perhaps the first mention of the concept of kavvanah:
היה רוכב על החמור, יירד; אם אינו יכול לירד, יחזיר את פניו. אם אינו יכול להחזיר את פניו, יכוון את ליבו כנגד בית קודש הקודשים.
If one is riding on a donkey [and the time comes to recite the Amidah], he should get down off the donkey. If one cannot do so, he should turn his face [toward Jerusalem]. If one cannot do this, then he should direct his heart toward the Holy of Holies [of the Temple in Jerusalem]. (Berakhot 4:5)
In some sense, we are all so distracted that we are figuratively riding on donkeys. And even though we might be praying while actually facing Jerusalem and the Holy of Holies, the direction of one's heart is even more important. Kavvanah is the way to direct your heart.