Meaning of " knowing"

What really means that you know something about it? Today's Rev. Bill's sermon reminded me a conversation with one of my friends. We shared one day about this real meaning of "knowing". We say lots of times " I know that". However, I question myself "do I really know it?" For example, if I know about that we need to exercises for our health, but do not exercise, it means I do not know the meaning exactly. Do you get my point? If we know something but not believe or follow it, it is not truly known by us. As same thing, we know that God loves us deeply and forever. However, we doubt and act like we do not know. It means that we really do not know. We can't say we know about it unless we truly act on it. It is tricky to explain but somehow true. I think that I assume that I know stuff but really.... I do not know them well enough to follow as knowledge. I have thought about it since this morning, what if I do everything what I say I know truly everyday then, what will happen? I must have been in good shape first of all in everything. I would eat only "good food", would exercises properly, sleep regularly, be done my dissertation, love always, pray in every moment, be gentle to everyone and so on. I really do want to follow at least a couple of things for sure that I know in truth and do action. I will try to do my best to keep my word that I say "I know."