Biblical Unknowability

One finds early hints to the idea of the unknowable God in the Pentateuch. The classic passage is found in Exodus 33, where Moses makes various entreaties of God which might be interpreted as part of a quest to understand the Divine nature. Moses asks, "Now, if I have truly gained Your favor, pray let me know Your ways, that I may know You and continue in Your favor," and a few verses later, "Oh, let me behold Your Presence."

To this, God famously responds as follows:

I will make all My goodness pass before you, and I will proclaim before you the name Lord, and I will grant the grace that I will grant and show the compassion that I will show. But, "He said, "you cannot see My face, for man cannot see Me and live." And the Lord said, "See, there is a place near Me. Station yourself on the rock and, as My Presence passes by, I will put you in a cleft of the rock and shield you with My hand until I have passed by. Then I will take My hand away and you will see My back; but My face must not be seen.

The metaphysical reading of this passage is either that God is in His essence somehow too "intense" to be directly perceived by human senses without damage to the perceptual apparatus, or, more abstractly, that God in His essence cannot be comprehended by mortal (i.e., living) creatures because His essence in some way transcends their representational or computational capacities. Both interpretations have been offered by various commentators, and sometimes (it would appear) even by the same commentator.

In Neviim and Ketuvim we find many additional passages that accommodate themselves to interpretations involving the unknowability of God. Kohelet claims in 3:11 that "He also puts eternity in their mind, but without man ever guessing, from first to last, all the things that God brings to pass," and later in 11:5, that "Just as you do not know how the life-breath passes into the limbs within the womb of the pregnant woman, so you cannot foresee the actions of God, who causes all things to happen." Likewise, The Psalmist proclaims (Ps.145) "Great is the Lord and much acclaimed; His greatness cannot be fathomed," and (Ps.147) "Great is our Lord and full of power; His wisdom is beyond reckoning." The Jewish Apocrypha also contains similar references to God's unknowability. From Ben Sirah 43:27 (skehan_dilella_87), we have

More than this we will not add;
let the last word be "He is the all."
Let us praise Him the more, since we cannot fathom Him,
[...]
Extol Him with renewed strength,
and weary not, though you cannot fathom Him.
For who has seen Him and can describe Him?
or who can praise Him as He is?
Beyond these, many things lie hid;
only a few of His works have I seen.

However, the passages most frequently cited in support of God's ultimate unknowability are those from Isaiah and Job:

Who measured the waters with the hollow of His hand,
And gauged the skies with a span,
And meted earth's dust with a measure,
And weighed the mountains with a scale
And the hills with a balance?
Who has plumbed the mind of the Lord,
What man could tell Him His plan?
Whom did He consult, and who taught Him,
Guided Him in the way of right?
Who guided Him in knowledge
And showed Him the path of wisdom?
[...]
To whom, then, can you liken God,
What form compare to Him?
[...]
Do you not know?
Have you not heard?
The LORD is God from of old,
Creator of the earth from end to end,
He never grows faint or weary,
His wisdom cannot be fathomed.
(Isaiah 40:12-28)

For My thoughts are not your thoughts, neither are your ways My ways, says the Lord. For as the heavens are higher than the earth, so are My ways higher than your ways, and My thoughts than your thoughts. (Isaiah 55:8-9)

Behold, God is great, and we know it not, nor can the number of his years be searched out. (Job 36:26)

Would you discover the mystery of God?
Would you discover the limit of the Almighty?
Higher than heaven — what can you do?
Deeper than Sheol — what can you know?
(Job 11:7-8)

Although all these Biblical passages are wonderfully pregnant with metaphysical possibilities, and have of course been the subject of uncountable interpretations of metaphysical character, it is not completely clear whether the biblical authors generally intended their words to be understood as claims about the unknowability of God. The context of some of these passages often makes it seem more plausible that they are intended to highlight the great power of God or his great fidelity and consistency, rather than speaking to metaphysical issues. (For example, "My ways are not your ways" because "the word that issues from My mouth...does not come back to Me unfulfilled, But... achieves what I sent it to do.")

There are certainly also many passages that seem to convey the contrary idea, that God can be known. For example, in Proverbs (2:1-5) we have,

My son, if you accept my words
And treasure up my commandments;
If you make your ear attentive to wisdom
And your mind open to discernment;
It you call to understanding
And cry aloud to discernment,
If you seek it as you do silver
And search for it as for treasures,
Then you will understand the fear of the LORD
And attain knowledge of God.

More significantly, it seems to me that the entire message of Tanach is the knowability of God, and that most Biblical authors therefore do not have a conception of God as being unknowable. Rather, in most cases, God communicates his desires and attitudes plainly enough, and without any great sense of mystery. Nevertheless, the extent to which the Biblical authors where actually interested in metaphysics is something that can be endlessly debated, and which probably will.