The way to know that God exists is to trust Him. The way to know that electricity exists is not by theory but by using it. Simply begin believing God, act on it and doubts will disappear. Live as if there were a God and you will know there is. Faith in God is our own natural ability made operative by the Holy Spirit. To use faith is to be led by the Holy Spirit. God is not “my faith in God”, but He comes to me when I am prepared to trust Him. Try today. It really works. God bless you.