According to Osho, the divine is called ineffable because reality itself cannot be captured in definitions; even simple things—love, beauty, sweetness, the color yellow—elude words. The divine is the totality and summit of these, so any description shrinks it into falsity. The wise therefore remain silent about what it is and instead indicate how to realize it through direct experience.
It’s like trying to explain the taste of sugar—you only know by tasting, not by talking.