Gregory the Dialogist

He is higher than heaven, what canst thou do? Deeper than hell, what canst thou know? His measure is longer than the earth, and broader than the sea. In that God is set forth as 'higher than heaven,' 'deeper than hell,' 'longer than the earth,' and 'broader than the sea,' this must be understood in a spiritual sense, inasmuch as it is impious to conceive any thing concerning Him after the proportions of body. Now He is 'higher than heaven,' in that He transcends all things by the Incomprehensibility of His spiritual Nature. …

Morals on the Book of Job, Book X ↗

Thomas Aquinas

One should also not be surprised if the Creator is not known if creatures are not perfectly understood, because even if creatures were perfectly known, the Creator would still not be. For a cause can only be perfectly known through its effects when the effects equal in power to the cause. This cannot be attributed to God. So he continues, "He is higher than the heaven and what will you do? He is deeper than hell and from what will you know him? …

Commentary on Job ↗

Bonaventure

The height of faith consists in understanding the eternal God, its depth, in knowing God made man. Of the first, it is written: "It is higher than the heavens; what can you do?" Concerning the second, there is added: "It is deeper than the nether world; what can you know?" The depth of God made man, that is, the humility, is such that reason fails. The height of God is beyond investigation.

Collations on the Hexaemeron, Collation 8 ↗