Rabbi Joseph B. Soloveitchik, Exaltation, G-d and Redeeming the Aesthetic

“It is impossible to imagine prayer without, at the same time, feeling the nearness and greatness of the Creator. His absolute justice, His Fatherly concern with human affairs, His anger and his wrath caused by unjust deeds. When we bow in prayer we must feel His soothing hand, and the infinite love and mercy for His creatures. We cling to Him as a living G-d, not as an idea, as abstract being. We are in His company and we are certain of His sympathy. There is in prayer an experience of emotions which can only be produced by direct contact with G-d.”

R. Zeev Wolf of Zhitomer, a disciple of the Maggid of Mezritch; in Ohr Ha'Meir

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"The Men of the Great Assembly" (Anshei K'neset ha'Gedola) established the twelve intermediate petitions of the Amidah--for health, sustenance, the fall of our oppressors, and so on, among the many things that we need. Yet, can there be any change in the divine will (Heaven forbid!)? Let it never be suggested that there is any change in the will of the Creator of all, as it says, "I am Hashem--I have not changed" (Malachi 3:6). Rather, the process really has to do with those who are the recipients (of God's blessings). 

Rabbi Dr. Nathan Lopes Cardozo – Siddur Nehalal beChol

"Modern man lacks the vocabulary to say what is in his heart. The prayerbook saved man's life just in time, before he suffered spiritual death."

Rabbi Ben-Zion Bosker, The Prayer Book (a.k.a "The Bosker")

"The function of prayer in all of its manifestations is to bring us closer to God, that we may more faithfully perform His will."