I'm not talking about the Van Morrison tune, either (though it is a fabulous song).
For the last few weeks I've been working my way through Interior Castle, St. Teresa of Avila's treatise on prayer. It's a book written conversationally and is to a great degree accessible; yet there does not exist an adjective available to express the depth of this work.
St. Teresa writes, "our thoughts, or it is clearer to call it our imagination, are not the same thing as the understanding. (4th Mansion, Ch. 1, #8)"
About 12 years ago, I took on this book, and got only to the halfway mark, and couldn't understand any of it. I could imagine much of what she described, but I couldn't even begin to grasp what she was talking about. I didn't know myself at all. It wasn't until six years later, when I was really examining my life for my annulment, that I began to really understand what St. Teresa was talking about, even in the first mansion, and it was a far cry from what I imagined. I'm learning--sometimes by leaps and bounds, other times in itty bitty baby steps--that prayer is far more than a "conversation with God".
To explain it would take volumes.