Ahmad Ibn `Ata'Allah
Your Saying 'God is Most Great' does not mean that He is greater than something else, since there is nothing else alongside of Him, so that it could be said that He is greater than it. Rather, the meaning of Allahu Akbar is that He is much too great to be perceived by the senses or for the depths of His Majesty to be reached by reason and logic, and indeed, that He is much too great to be known by an other-than-Him for truly, no one knows God but God.
(Paraphrased As long as an individual's heart is filled with the tendency towards what is other-than-God Most High, there is no Certitude about God.) When certitude about God Most High does occur in the heart ... the heart becomes tranquil through the Majesty of God then it abstains from what is other-than-God. So, it stands weak and is compelled to cry out to God for help. Then He who responds to the necessitous when they cry out to Him, responds to it. That radiant light settles into the heart and the darkness of preoccupation with what is other-than-God is extinguished therewith. Then the reality of the Realm (al-Malakut) becomes visible to it, and that is what Harithah meant when he said to the Messenger of God 'It is as if I see the Throne of my Lord distinctly.' And the Messenger of God said, 'The Light of God Most High is faith in one's heart.'
Let your invocation be the all-embracing Name, which is Allah, Allah, Allah, or if you so wish, Huwa, Huwa, Huwa and do not violate this remembrance. Be careful lest your tongue pronounce it while other-than-He is in your heart. Let your heart be the one who utters, and your ear the one who is attentive to this invocation until the 'speaker' emanates from your Self (sirr). When you feel the emergence of the Speaker within you through the invocation, do not abandon the spiritual condition wherein you find yourself.