Four Great Vows of Bodhisattvas, Second Vow

Sentient beings are innumerable;
I vow to help them all.
Afflictions are inexhaustible;
I vow to end them all.
Dharma doors are boundless;
I vow to master them all.
Buddhahood is supreme;
I vow to attain it.

As long as we have afflictions, our minds will be impure and we will not be able to selflessly help others.

So the second vow is to end our afflictions, the causes of suffering. Desire, anger, ignorance, arrogance, doubt, and wrong views are the major afflictions—the six poisons. 

What is our ultimate reason for ending afflictions? Because we want to help innumerable beings. There are so many beings waiting for us to help them end their suffering forever. How can we do so if we have no virtues, no knowledge, and no abilities? The reason we vow to end afflictions, cultivate virtues, extensively learn Dharma doors, and attain Buddhahood, is for the purpose of universally helping all beings. It is not for ourselves. This is the force of great compassion.