“And so, let the faithful adore God with a mind that is not overcurious. And believe that He is God in three hypostases, although the manner in which He is so is beyond manner, for God is incomprehensible. Do not ask how the Trinity is Trinity, for the Trinity is inscrutable.
“But, if you are curious about God, first tell me of yourself and the things that pertain to you. How does your soul have existence? How is your mind set in motion? How do you produce your mental concepts? How is it that you are both mortal and immortal? But, if you are ignorant of these things which are within you, then why do you not shudder at the thought of investigating the sublime things of heaven?”
St. John of Damascus, On Heresies, Chapter 103.
(H/T to commenter Daniel D.D. on The TOF Spot.)