Three images, each more opaque than the last. Smoke covers fire — the fire is still there, just hidden temporarily. Dust covers a mirror — the reflection is distorted, and you need to clean it off. A membrane covers the embryo — the covering is thick, and the being inside must grow through it.
Knowledge is like that fire, that mirror, that embryo. It exists within every soul. Desire does not destroy it. It conceals it. Depending on how thick the veil of desire is, the effort to uncover the knowledge varies. Sometimes it takes a gentle wipe. Sometimes it takes sustained inner work over a long time.