“All our scientific and philosophic ideals are altars to unknown gods.”

Treatise on Demonstration of Problems of Algebra (1070).
Context: By the help of God and with His precious assistance, I say that Algebra is a scientific art. The objects with which it deals are absolute numbers and measurable quantities which, though themselves unknown, are related to "things" which are known, whereby the determination of the unknown quantities is possible. Such a thing is either a quantity or a unique relation, which is only determined by careful examination. What one searches for in the algebraic art are the relations which lead from the known to the unknown, to discover which is the object of Algebra as stated above. The perfection of this art consists in knowledge of the scientific method by which one determines numerical and geometric unknowns.

"The Singularity," The New Humanists: Science at the Edge (2003)

Variant: The future has many names: For the weak, it means the unattainable. For the fearful, it means the unknown. For the courageous, it means opportunity.
Source: Les Misérables

Source: The Halakhic Mind, 1986, p. 5

Source: Darwinia (1998), Chapter 15 (p. 136)

Source: Learning the World (2005), Chapter 4 “A Moving Point of Light” (p. 51)

Source: Democracy Ancient And Modern (Second Edition) (1985), Chapter 1, Leaders and Followers, p. 6

The Epistle to the Romans (1918; 1921)
Context: We know that God is He whom we do not know, and that our ignorance is precisely the problem and the source of our knowledge. The Epistle to the Romans is a revelation of the unknown God; God chooses to come to man, not man to God. Even after the revelation man cannot know God, for he is ever the unknown God. In manifesting himself to man he is farther away than before. <!-- p. 48