"Perception is temporary. It is an attribute of the space-time belief, and is therefore subject to fear or love. Misperception produces fear, and true perception induces love. Neither produces certainty because all perception varies. That is why it is not knowledge.....but knowing is the affirmation of truth."
When I perceive anything, it is coming from my own mind and from my belief system. So, as my beliefs change, what I perceive will vary....and that is why perceptions may produce fear or love and are temporary.
Truth, on the other hand, is steady, changeless, as God is.
Knowing is certainty. You can count on it. No one can take it away from you. Because you know. It's experience.
I remember a conversation I had once with a dear friend who asked me how could I be sure that God existed. I could not say anything convincing to prove the existence of God to them because my knowing came from experience. It started with faith, but ultimately it became a knowing. This no one and nothing could take away from me. That was exactly what I said to my friend. I know. I have experienced God but I can't explain it or prove it to you. It's personal and available to all of us as we desire it. And we will eventually. It is what we search for.