So much is wrapped up in this one little word. It could be referring to actual knowledge empirical facts and figures, the experience knowledge that one only fully grasps after they themselves have experienced something.
When we talk about knowing peace that comes from Jesus, it is more than existential understanding, but faith he gives. “It is by grace you have been saved,” Jesus makes us alive and gives us faith, and Jesus says, “Come, follow me…” inviting us to walk with him, learn from him, know him and what he has done for us.
Knowing his grace and forgiveness for us, gives us peace.