Real Exsience

Locke says we have no real knoweldge of what "real exsience" is. At first i didnt understand what he meant by this but then realized he was talking about a higher being (ex. God). I guess he means that we cant really understand the higher being since he earlier said we all can imagine a God. I can totally see how he would think this since his idea is seeing something is the only way you can get that image in your mind. So maybe he is right we really dont have a good understand of what god really is or how great he is.