The poem sheds light on the beginning and end of life. The circle that every thing and everyone goes through birth and death. The beauty of life and the ineffability of death and end. The changes we go through and the things in life that stay the same. We are like a stream that constantly flows and affects those around us. It's a beautiful thing, life and death.
The author uses a lot of personification to compare the flow of water to humans. "Life's parting stream descends" Life takes many turns.
He uses many visually descriptive words to really describe the the mountain over the ocean and the sunshine touching the water.
The metaphor , From the same cradles side makes the reader feel a cozy and warm feeling.