Regarding God entering the universe, the hand in cookie jar is not an appropriate analogy.  Firstly you and the cookie jar are in the same dimension.  Secondly, you hand (the part that goes in the jar) is smaller than the opening of the cookie jar.  Both these are not valid when it comes to God.  Suppose you were so big that only one blood cell of yours could enter the cookie jar. No one would know that the blood cell represented you.  You know what I am trying to get at.

 

Again, the idea is not for God to prove HE exists.  Anyone with half a brain, who uses a little bit of it, knows God exists. It is for us to realize that God Alone is Lord and Master without seeing HIM (if we were to see HIM their would be no decision required on our part).

 

The statement 'if you believe no proof is necessary' is scary. Believe what? That God exists?. Like I said, many people of different religions believe God exists, but they do not do that without associating another entity like Jesus, Muhammad, Buddha, the saints etc. and giving it power.  The proof is not for God's existence but that there is no god but God - something the vast majority of mankind who believe in God has missed.