John Denver – Boy From The Country lyrics

It is about St Francis of Assisi. The talking and communicating with the animals, leaving his home and the people thinking he was insane is exactly what St Francis did. He believed that he could talk to animals and they could talk to him. He understood so much about life and nature. He did not believe that you needed to go to church to be in Gods presence and that Nature was where God lived as well as in Heaven. He did not believe in material riches and things and actually gave up all his worldly things to live in nature and was a true minimalist. He came from a very wealthy home his father being a textile merchant from Assisi - people couldn't understand why he would give up all the comforts money brings to basically live in the forest with only the clothes on his back. His robe that he made was constructed of bits and pieces of many types of garments and materials. Whatever he could find and he made it himself.
Also "he called the forest brother... he called the Earth his Mother" are indicative of St Francis as well. He believed that God was in everything and that we must care for the Earth and its inhabitants. He was like the first Ecologist in addition to his spirituality. He actually was made a Saint (I believe) within two years of his death which is unusual for the church to do.