That which I can possibly understand is not the Divine.
We have here a negative sort of definition.
This is a warning to a category of persons who are self-deluded by their commonsense logic into believing that they have achieved a certain grasp of what God is.
God is that which cannot be grasped, and any claim to have done so can only be mistaken.
It is like saying that one has grasped the horizon.
There are the biblical accounts of Moses and Isaiah or any of the prophets, but that is a matter of another kind of vision.
Moreover, what Moses saw may have made him the humblest of men, but he was quite explicit in saying that man cannot see God and live.
–Rabbi Adin Steinsaltz