If a bodhisattva obliges all sentient beings, then he is also obliging, and making offerings to all buddhas.
If he honors and serves all sentient beings, then he is also honoring and serving the Tathagathas.
If he gives happiness to all sentient beings, then he is also providing happiness to all buddhas.
Why is it so? Because the mind of great compassion is the essence of all buddhas. Because there are sentient beings, great compassion develops. And from great compassion, the Bodhi mind is brought forth. And because of the Bodhi mind, buddhas attain perfect enlightenment.

── from Sishi Huayan
(Forty-Fascicle Avatamsaka Sutra)

The bodhisattvas, mahasattvas* observe sentient beings through the ten contemplations and give rise to the mind of great compassion. What are the ten? They are:

Giving rise to great compassion when seeing sentient beings without reliances;

Giving rise to great compassion when seeing sentient beings with hearts in discord;

Giving rise to great compassion when seeing sentient beings lacking wholesome roots;

Giving rise to great compassion when seeing sentient beings in their long slumbers;

Giving rise to great compassion when seeing sentient beings doing unwholesome deeds;

Giving rise to great compassion when seeing sentient beings shackled by desire;

Giving rise to great compassion when seeing sentient beings drowning in the sea of life and death;

Giving rise to great compassion when seeing sentient beings constantly surrounded by pain and suffering;

Giving rise to great compassion when seeing sentient beings without yearning for the wholesome Dharma;

Giving rise to great compassion when seeing sentient beings lost and without the Dharma.

── from Bashi Huayan
(Eighty-Fascicle Avatamsaka Sutra)
* Mahasattvas, meaning “great beings,” is another name for bodhisattvas.