St. Augustine of Hippo talks about some of his misconceptions of God in his Confessions, and that is one of them. God is not comprised in the universe, and he does not have any type of spatial extension in his divinity.
God is infinite insofar as he is not bounded or conditioned.
St. Thomas Aquinas wrote that God is omnipresent not because he has spatial extension everywhere, but because all things at all times have God as their cause, and a cause is always present in some fashion to its effects.
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