I posted this at Wikipedia:
According to Ratzinger, if the question of the knowability of God is not addressed, then “agnosticisim would in fact be the only correct attitude for man,” an “honest and devout” acknowledgement of that which eludes our field of vision. Ratzinger (later elected as Pope Benedict XVI) also cautions against a premature objection to agnosticism, one that is merely based on affirming man's “thirst for the infinite.” He says that the best critique lies in the practical realm.
The true way to call agnosticism into question is to ask whether its program can be realized. Is it possible for us, as human beings, purely and simply to lay aside the question of our origin, of our final destiny, and of the measure of our existence? Can we be content to live under the hypothetical formula “as if God did not exist” while it is possible that he does in fact exist? (...) I am forced in practice to choose between two alternatives: either to live as if God did not exist or else to live as if God did exist and was the decisive reality of my existence. What is at stake [in agnosticism] is the praxis of one’s life.
Ratzinger thinks that human reason has the power to know reality, and attain the truth. For this, he alludes to the achievements of the natural sciences. He believes that agnosticism is a self-limitation of reason rooted in Kant: reason imposes limits on itself which can lead to dangerous pathologies of religion, such as terrorism and pathologies of science, such as ecological disasters. He thinks that this self-limitation dishonors reason and is contradictory to the modern acclamation of science, whose basis is the power of reason.
When people argue that God is unknowable because he cannot be experienced and tested scientifically, Ratzinger differentiates God from other knowable objects:
This question regards not that which is below us, but that which is above us. It regards, not something we could dominate, but that which exercises its lordship over us and over the whole of reality.
[To] impose our laboratory conditions upon God...implies that we deny God as God by placing ourselves above him, by discarding the dimension of love... [To think thus] would make God our servant.
There are many things that we do not see but they exist and are essential...We do not see our intelligence and we have it: we do not see our soul and yet it exists and we see its effects, because we can speak, think and make decisions.
Ratzinger thinks that there is a natural knowledge of God "through the things he has made," and agrees with Paul of Tarsus that “agnosticism that is lived out as atheism” is not “an innocent position.”
Agnosticism is always the fruit of a refusal of that knowledge which is in fact offered to man… Man is not condemned to remain in uncertainty about God. He can “see” him, if he listens to the voice of God’s Being and to the voice of his creation and lets himself be guided by this. The history of religions is coextensive with the history of humanity. As far as we know, there has never been an epoch in which the question of the One who is totally other, the Divine, has been alien to man. The knowledge of God has always existed.
See Wikipedia on Agnosticism