Bhagavad Gita, Chapter 9, Verse 2

Of sciences, the highest; of profundities, the deepest; of purifiers, the supreme, is this; realisable by direct perception, endowed with immense merit, very easy to perform, and of an imperishable nature.

This knowledge gets described with a real, specific list of qualities, not vague spiritual praise.

Naming it purifying, direct, practical, and lasting all at once gives real, concrete shape to what's otherwise an abstract claim. Real value here is described as something that can actually be checked, not just taken on faith.