'I know for sure that I exist'
Descartes
You believe that you know for sure that you exist. Descartes said, "I think, therefore I am." However, it was a famous atheist - Bertrand Russell - who pointed out why the statement is wrong. Descartes got it wrong because in the first premise it is assumed that "I" exist.
So what is actually being said is - I am, and I think, therefore I am - which is clearly viciously circular. So unless you start with God you can't even know that you exist because you can't justify your belief.
And even if for the sake of the argument I were to grant that you know that you exist (which you don't without God) - so what?! Where do you go from there? Rocks exist, but they don't do any thinking and don't know anything.
"Knowing" that you exist (and "knowing" you are not God) provides no real basis for any knowledge. So without God you are in the absurd position of not knowing anything. But do you know that?
So what is actually being said is - I am, and I think, therefore I am - which is clearly viciously circular. So unless you start with God you can't even know that you exist because you can't justify your belief.
And even if for the sake of the argument I were to grant that you know that you exist (which you don't without God) - so what?! Where do you go from there? Rocks exist, but they don't do any thinking and don't know anything.
"Knowing" that you exist (and "knowing" you are not God) provides no real basis for any knowledge. So without God you are in the absurd position of not knowing anything. But do you know that?
The question you must face is - how do you know your reasoning is valid?