We can know God and not run through our lives with an abstracted belief system based upon assent to a theoretical proposition. God is not into theory in a big way. God wants to Know and be Known, to stop at the question of whether or not God exists is a poor substitute for living, moving and having your being in the divine life of God. Because they do not match the requirements of Empirical knowing they are discounted. Even as our holy texts speak of them, the body of tradition attests to them, they proven and time tested, we doubt them.
Spiritual knowing is experienced based.
You have to do it to know it. Christian knowing of God includes two vital elements, discernment of call and discernment of the Spiritual gifts necessary to equip the call. An excellent resource in learning how to hear God's call is Listening Hearts by Farnham, Gill, McLean and Ward. Listening with every fiber of our being, body and spirit. Prayer that is receptive and listening.