The cavemanesque simplicity is not the drawback, it's the appeal.
Pierce the skin of a human being, and "blood and water" is what you get, which is what the Bible says came from the side of Jesus Christ, when the Roman soldier pierced it.
But the average human being is no Jesus. By substituting the word "mud" for "blood" in the phrase "blood and water," you remind us that most people are more earth bound than divine.
Aspiration is rough, it's full of effort and failure. It's stressful.
By laying down in the rain, we temporarily take a breather from aspirations. We accept our humble situation, and by allowing "mud" to "flow through" our "veins," we accept our basic selves.
Self-acceptance is at the heart of your song.
And a desperate, primitive, tribal drumbeat, layered with the yearning rhythms of gospel, suggests that the primitive and divine in a human being unite in that moment of humble self-acceptance, as you crumble to the floor and allow mud and rain to wash through and over you.
The very act of self-acceptance becomes a ritual from which you can draw strength, get up again, and walk on, reinvigorated with new strength and new aspirations.
Great song! Take strength from your own song, and walk on in your new life, brother. :)