After the binding of Isaac, כִּי עַתָּה יָדַעְתִּי כִּי־יְרֵא אֱלֹהִים אַתָּה — “now I know that you fear God?” What does this passage really mean?
The verse would seem to imply that God did not know whether Abraham feared God. But, now as a result of the Akedah, God’s personal knowledge has been expanded. But such a limited view of omniscience was something many rabbis found theologically scandalous, for how can a human being grasp the nature of God’s omniscience, since God’s thoughts are higher than man’s (Isa. 55:9). Ramban offers a more sober theological answer. Abraham’s “awe of God” existed only in potentia, but now as a result of his [selfless] deed, his “awe of God” became actualized. Some scholars bypass this theological question altogether. Rashi paraphrases the verse to mean “Now I can give reason why I love you.” This use of “know” may parallel the use suggested in Genesis 4:1, where the text says, “And Adam knew Eve . . .” There, the expression clearly implies intimacy; by the same token, here too, God was intimate with Abraham.
What it means to “fear God”? The Hebrew concept of yare, when used in association with God denotes something far more profound. Most importantly, “fearing God” means more than having a sense of awe or reverence; it also involves a kenosis an emptying or surrendering to the mysterious will of the Divine. Martin Buber develops this important theme in his book, The Eclipse of God. Many of his ideas provide an important perspective to understanding the visceral power of the Akedah and its historical effect in shaping the Jewish psyche. Buber writes:
All religious reality begins with what biblical religion calls the ‘fear of God.’ It comes when our existence between birth and death becomes incomprehensible and uncanny, when all security is shattered through the mystery. This is not the relative mystery of that which is inaccessible only to the present state of human knowledge and is hence in principle discoverable. It is the essential mystery, the inscrutableness of which belongs to its very nature; it is the unknowable. Through this dark gate (which is only a gate and not, as some theologians believe, a dwelling) the believing man steps forth into the everyday which is henceforth hallowed as the place in which he has to live with the mystery. He steps forth directed and assigned to the concrete, contextual situations of his existence. That he henceforth accepts the situation as given him by the Giver is what Biblical religion calls the ‘fear of God.’ 
. See Gersonides and Brueggemann.
.Many Jewish exegetes since the time of Saadia, Ramban and Rashbam, understood the verse ”for now I know that you fear God,” as meaning: “for now I see it and I have made known to all humankind that you are a God fearing man” The problem with this reading is that the verb “I have known” is not written in the Hiphal, but is written in the Qal perfect.
.The term “mystery” as used here does not denote an unsolved-puzzle or a gap in our knowledge. Rather it refers to something that is inherently unknowable and inexplicable. No amount of knowledge can ever diminish or eliminate the sense of mystery. On the contrary, it intensifies it. It is the source of all wonder, and lies at the root of true worship and devotion. This sense of mystery evokes questions that point us towards ultimate issues and ultimate concerns.
.Martin Buber, Eclipse of God (New York: Harper & Brothers, 1952. p. 36b.