If you make sentient beings happy, you make all Buddhas happy. Why? Because the heart of great compassion is the substance of the Buddhas. Therefore they develop great compassion on account of sentient beings, develop the will for enlightenment based on great compassion, and attain true awakening on the basis of the will for enlightenment. It is like a giant tree in a desert; if the roots find water, then the branches, leaves, flowers, and fruits all flourish. The giant tree of enlightenment in the desert of birth and death is also like this. All living beings are the root of the tree; the Buddha and bodhisattvas are the flowers. Benefit living beings with the water of great compassion and you can obtain the flowers and fruits of knowledge and wisdom of Buddhas and bodhisattvas.
~The Avatamsaka Sutra