You don't know about the existence of God that is specific... but also, you don't know that spiritual things can only be discerned only by people 'alive' or with his spirit, and no amount of words someone can tell to you is going to make you understand because you need first to br alive with the spirit of God, and like the bible says this is crazyness for the people who don't believe or are spiritually dead (not having their spirit alive with the spirit of God).
There is lots of stuff, like when Jesus said people would have water of life, this is something a christian can get and gives you satisfaction and calms your spiritual hunger when he gives it to you, or that the holy spirit is very gentle, and sensitive, and caring, and after tasting how he is, you can't think of a person in the universe better than him, because he is so nice. And you can't know this if you didn't had any experience with him, is like someone telling you a person is nice, but you don't meet the person, you can only imagine things.
But probably this stuff appears to unbelievers as something to be made fun of, or that comes from crazy or deluded people. So i don't know why i'm trying to tell them to you.