Like mistysan said, this song is about losing someone/dying. The way the song is sung is very interesting because it gives you the idea that either a parent, or some type of care giver is singing the song. "The sun will set for you." Well ya, that's saying that your going to die soon. "The shadow of the day will embrace the world in gray." this is referring to the dying person's death will make close ones sad, or embrace them in depression. "Sometimes goodbye's the only way." is saying that the person is to damaged or ill to live any longer, or he/she is in great pain. "The only way", saying that the only way for peace for everyone. Now more so for the dying person than everyone else, but eventually they will be at peace with nature again and that they don't have to worry about him/her being in pain any longer.