The fact of God’s existence is known, but it is not in our power to grasp His essence. The cognitive achievement is to fully comprehend our inability to know God.

As the wise person said when he was asked whether he knew God’s essence, “If I knew Him, I would be Him.” No one can grasp God’s essence except for God Himself, although His existence is revealed by His works in a complete manner. Praiseworthy is the One who, in His perfection, has surpassed us, and whose mighty appearance is concealed from us, just as perception of sunlight and its pleasantness is concealed from those who have weak eyesight. Their inability [to see it] does not indicate its nonexistence. All that we can comprehend of God is that it is impossible to comprehend Him. As the wise person said, “The entirety of what we know of You is that we cannot know You.” (Rav Yosef Albo, Sefer HaIkkarim 2:30)

The commandment to have faith means gaining as much of an understanding of the Creator as possible, and to have faith with regard to everything that cannot be understood.

Therefore, King David states, “Know the God of your father” (I Chronicles 28:9). “Know” means that you must strive to grasp every aspect of His godliness that can be grasped in terms of knowledge, and consider these matters in depth. This is the knowledge of His existence and the fact that He is the source of life…. With regard to that which is impossible to grasp with knowledge [rational understanding], have it rest upon faith. Trust in Him with complete faith once you know of His existence and the fact that He is the source of life. Faith is a genuine experience like visual perception. Thus, that which is impossible to grasp [intellectually] is experienced as faith. (Tzemaĥ Tzedek, Derekh Mitzvotekha 46a)