You all know "Footprints," right, about the footprints in the sand with the payoff when God says, "Then I carried you."?
It has been observed that, the first time you hear it, it's devastating; after half a dozen listens, you reply with a somewhat stiff, "Yes, I am familiar with that particular allegory"; and eventually you don't even notice the "Footprints" trivet on the clearance table at the local Christian books and gifts store.
This seems to be the way of all human wisdom. Sooner or not much later, we get to the bottom, and attempts to distill additional wisdom are frustrating.
When you construct something with a profound payoff, it eventually pays off all it has. Things written for effect soon lose their effect, and then they are good for nothing but trampling underfoot.
Now, Chesterton once complained about complaints that writers who "wrote for effect." He wondered what the devil they should write for? Effectlessness? But a writer getting read once is more than he can ask for, and getting reread is very heaven. That the well runs dry after four times through is not, generally, their concern.
Scripture is different. As part of God's revelation to man, it is to be read and reread, heard and reheard. For the most part, it doesn't pop at you on first reading, so it doesn't go stale on you on tenth reading.
But it does go opaque. It's kind of strange, isn't it, how a familiar passage doesn't become dull so much as silent. They don't tell you what you already know; they simply don't tell you anything at all. And of course there are passages that are silent from first reading on.
And then... pop! "The servant must have told the father his eldest son wouldn't come in to the celebration. I can be that servant, praying to God that my too-proud friend might return to the Church." Or whatever. A whole new vein is discovered, and the passage becomes a profitable mine once more. (I've lost all control over the metaphors in this post.)
In my experience, this process recurs often enough that one is soon convinced it will not end in this life, that the wisdom of God contained in the Bible is indeed without limit, that its cup cannot be drained.