Because it is God’s creation

Beyond doubt, [St.] Francis not only praised God’s gracious love bestowed on Francis, but showed concern for all of God’s creatures as well. It sprang from a sense of gratitude for God’s continuing gifts to Francis and all people. Francis probably didn’t know the word “ecology.” But he showed a consistent love for creation because it is God’s creation. He knew that relationship to God included a universal relationship to all of God’s creatures. They became his brother and sister.

~ Lester Bach, OFM Cap, The Franciscan Journey: Embracing the Franciscan Vision

Laudato Si: The heart of what it is to be human.

[St.] Francis helps us to see that an integral ecology calls for openness to categories which transcend the language of mathematics and biology, and take us to the heart of what it is to be human. Just as happens when we fall in love with someone, whenever he would gaze at the sun, the moon or the smallest of animals, he burst into song, drawing all other creatures into his praise. He communed with all creation, even preaching to the flowers, inviting them “to praise the Lord, just as if they were endowed with reason”.

~ Pope Francis, Laudato Si (Praise be to you – On Care For Our Common Home), Paragraph 11

Laudato Si: The example par excellence

I do not want to write this Encyclical without turning to that attractive and compelling figure, whose name I took as my guide and inspiration when I was elected Bishop of Rome. I believe that Saint Francis is the example par excellence of care for the vulnerable and of an integral ecology lived out joyfully and authentically.