Actually the religious texts are full of koans, not just zen buddhism, hindu texts, bible also etc. Its a revelation of truth, put in words. Its just that it cant be understood without spiritual intuition. Hence a riddle to most. And plain obvious to some... I would say the upanishads are full of them.
A funny example:
Kau****aki-Brahmana Upanishad 3.2
Then he (Indra) said: I am the Spirit of the vital breath [Prāṇa], the intelligent Self. As such, worship me as life, as immortality.
Brahmna sutra 1.1.28 remarks:
Prāṇa is Brahman, because it is comprehended thus [interpreted as Brahman in the above verse].
(I.e. since Indra is enlightened he talks about his self as Brahman)
Then compare to the famous (but so misunderstood) Bible koan, John 14:6:
Jesus answered, "I am the way and the truth and the life. No one comes to the Father except through me."
Most christians will interpret it as only through worship of Jesus can you get to heaven.
But apply the Brahman sutra interpretation (or intuition) and you get:
"Brahman is the way and the truth and the life. No one comes to Brahman except through his own self (knowing atman as brahman)"
And that concludes todays lesson on koans
Peace!