It is a problem that humanity knows only very few facts about God for sure. Some things from natural theology, like that there must be a God. But even if we accept historical knowledge about Christianity as reliable enough to accept it as facts, there are not so many facts. Because one needs to keep away from non-sober, speculative interpretations of the Bible that are employed in most sermons; see also my post on that: “Get sober, Christian fellows“.
This situation is far away from both knowing something factually in detail (as in natural science) and from knowing somebody personally in detail (as in relationships). Not quite satisfying, huh?