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.
The fourth vow, the attainment of enlightenment, of Buddhahood is our ultimate goal. Only as a Buddha, can we perfectly fulfill the four vows. Only as a Buddha, will our generosity, morality, patience, diligence, meditative concentration, and wisdom finally be perfected. Only as a Buddha, will our vow to help all beings be perfectly fulfilled and our afflictions perfectly eliminated.
With this fourth vow, we will know our ultimate goal. The second and third vows provide the road map to arrive at our goal. Without this road map, we will not know how to progress or even what direction we are headed in.
The first vow provides us with our motivation—we make the vow that we will help all beings end suffering and attain happiness.