The Maharal asks a fundamental question in the beginning of Nesiv Avodah: Since
The Benefits of Speech
One advantage that speech has over thought is that it aids one’s concentration and enhances comprehension. For this reason the Rabbis teach to praying aloud (See Shulchan Aruch Orach Chaim 101:1, where the poskim discuss raising one’s voice during prayer to help the person concentrate better).
In yet a deeper sense, prayer causes one to change:
Rabbi Shimshon Raphael Hirsch writes that the root word for “prayer” (פלל - peh lamed lamed) means “to judge”. “To pray” (“lehitpalel” in Hebrew, a reflexive verb), thus means “self-judgment”. Prayer requires a truthful self-analysis, and introduces the worshipper to a new perspective of his inner makeup and of his life situations. Encountering
This process of self-judgment becomes much more powerful when expressing one’s thoughts in words. By being forced to “confront” the audible, self-analysis brings one to ultimate change.
One reason for this is that the faculty of thought is not used to communicate with others. Rather, it remains hidden from all. It was not created to be part of the physical realm. With respect to man’s perspective of the self, hidden in one’s mind, it is more likely for a person to perceive himself in a way that is not true. However, listening to those same thoughts made audible, even by the person himself, will be far less “tolerable”. The spoken word will have a better chance of being rejected if it is not really true. Perhaps this is because audible speech is a real part of the physical realm, and meant to be communicated to someone else. Therefore, a person is more embarrassed by the things he actually says, and not (as much) by what he thinks.
In connection to the above point, the Maharal of Prague explains why one must express his prayers specifically through speech, and not simply through contemplation or meditation. When one expresses himself through speech he invests his vitality and soul into his words. These words in turn ascend upon high (Zohar). As a result, when one prays it is considered as if he had given a portion of his very soul “above”. In this respect one’s prayers, which were instituted in place of the Temple service (Berachot 26b), resemble a sacrifice, which was offered to Gd on the mizbe’ach, the altar. Through the spoken word of prayer we offer up our soul to