Rather than seeing nature and its elements merely as inanimate objects to be used and exploited by us humans, St. Francis of Assisi understood the whole world as relational, sister, mother, and brother with God as Father. For Francis, created by the 'Most High, good Lord' meant that everything must possess God's goodness in some way, and so for him each thing however great or small has an inherent dignity. St. Francis related to and interacted with the world in the light of this insight.
As 'Mother', the Earth cares for all our needs providing us and the other creatures of the earth with plenty to sustain us all, and as 'Sister', we have a responsibility to care for the Earth as we would wish to care for our very own blood sister. But St. Francis realised that as mother, sister & brother, the earth with all its creatures has another role too, that of guiding and leading us towards God ...
One of St. Francis of Assisi's legacies was his great insight that God reveals Himself in the beauty and diversity of nature. As such, creation is the primary revelation of God, and St. Francis loved it because he saw in it, God's handiwork. He would say that these insights came to him from God, and they dawned on him as he gazed at the created universe around him, at the flowers and the birds, at the moon and the stars, at the people with whom he interacted, reflecting all the while on the love and generosity of God in creating such wonders.
Since nature was created by the "Most High, all-powerful, good Lord," Francis began to see God's goodness at the heart of all matter. He came to believe that all creation is sacred and points beyond itself to its Creator, God. Francis has been described as a nature mystic because he allowed nature to guide him towards God. We too, by God's grace, can be led to God if we look deeply and reverently at His creation, at leaves, insects, the rain, people, stones etc.