As one contemplates, penetrating deeper and deeper into the nature of reality, one leaves the sensible world behind, transcends the subject/object mode of perception, and experiences one's soul.
There is a mystery about rivers that draws us to them, for they rise from hidden places and travel by routes that are not always tomorrow where they might be today. Unlike a lake or sea, a river has a destination and there is something about the certainty with which it travels that makes it very soothing, particularly for those who've lost faith with where they're headed.