6 For such an indication of God's infinity the words 'I Am that I Am ' were clearly adequate; but, in addition, we needed to apprehend the operation of His majesty and power. For while absolute existence is peculiar to Him Who, abiding eternally, had no beginning in a past however remote, we hear again an utterance worthy of Himself issuing from the eternal and Holy God, Who says, Who holds the heaven in His palm and the earth in His hand, and again, The heaven is My throne and the earth is the footstool of My feet.
What house will you build Me or what shall be the place of My rest ? The whole heaven is held in the palm of God, the whole earth grasped in His hand. Now the word of God, profitable as it is to the cursory thought of a pious mind, reveals a deeper meaning to the patient student than to the momentary hearer. For this heaven which is held in the palm of God is also His throne, and the earth which is grasped in His hand is also the footstool beneath His feet. This was not written that from throne and footstool, metaphors drawn from the posture of one sitting, we should conclude that He has extension in space, as of a body, for that which is His throne and footstool is also held in hand and palm by that infinite Omnipotence.
It was written that in all born and created things God might be known within them and without, overshadowing and indwelling, surrounding all and interfused through all, since palm and hand, which hold, reveal the might of His external control, while throne and footstool, by their support of a sitter, display the subservience of outward things to One within Who, Himself outside them, encloses all in His grasp, yet dwells within the external world which is His own. In this wise does God, from within and from without, control and correspond to the universe; being infinite He is present in all things, in Him Who is infinite all are included.
In devout thoughts such as these my soul, engrossed in the pursuit of truth, took its delight. For it seemed that the greatness of God so far surpassed the mental powers of His handiwork, that however far the limited mind of man might strain in the hazardous effort to define Him, the gap was not lessened between the finite nature which struggled and the boundless infinity that lay beyond its ken, I had come by reverent reflection on my own part to understand this, but I found it confirmed by the words of the prophet, Whither shall I go from Your Spirit?
Or whither shall I flee from Your face? If I ascend up into heaven, You are there; if I go down into hell, You are there also; if I have taken my wings before dawn and made my dwelling in the uttermost parts of the sea (You are there). For there Your hand shall guide me and Your right hand shall hold me</em>. There is no space where God is not; space does not exist apart from Him. He is in heaven, in hell, beyond the seas; dwelling in all things and enveloping all. Thus He embraces, and is embraced by, the universe, confined to no part of it but pervading all.
Source: On the Trinity (New Advent)