Know that firm in knowledge are those who refrain from...
Know that firm in knowledge are those who refrain from opening the curtains that lie against the unknown, and their acknowledgement of ignorance about the details of the hidden unknown prevents them from further probe. Allah praises them for their admission that they are unable to get knowledge not allowed to them. They do not go deep into the discussion of what is not enjoined upon them about knowing Him and they call it firmness.
Be content with this and do not limit the Greatness of Allah after the measure of your own intelligence, or else you will be among the destroyed ones.
He is Powerful, such that when imagination shoots its arrows to comprehend the extremity of His power, and mind, making itself free of the dangers of evil thoughts, tries to find Him in the depth of His realm, and hearts long to grasp realities of His attributes and openings of intelligence penetrate beyond description in order to secure knowledge about His Being, crossing the dark pitfalls of the unknown and concentrating towards Him He would turn them back.
They would return defeated admitting that the reality of His knowledge cannot be comprehended by such random efforts, nor can an iota of the sublimity of His Honour enter the understanding of thinkers.