This quote is from Master Hsuan Hua‘s commentary on the Medicine Master Sūtra.

We were born from ignorance. Ignorance is the root of birth and death, the source of all troubles and afflictions. The goal of our practice is to break through ignorance. Ignorance confuses us, so that we live as if drunk or dreaming, driven by the desires for wealth, sex, fame, food, and sleep. Ignorance causes us a lot of trouble. Once there is ignorance, it manifests in activity. We act on what we don’t understand, and then we become attached to appearances. When consciousness arises and begins to make distinctions, the marks of self, others, living beings, and a life span appear. Activity and consciousness generate name and form, making it possible to talk about things. Then the whole body comes into being, and with it, the six entrances (eyes, ears, nose, tongue, body, and mind). The six entrances come into contact with the external environment, and that contact brings on feeling. We differentiate between good and bad sensations, trying to avoid unpleasant sensations while craving pleasant ones. Thus, feeling then brings on craving. As we grasp at the object of our craving, there is becoming, then birth into the next life, and then old age and death all over again. The Twelve Links of Conditioned Causation describe the endless rounds of rebirth that all living beings undergo.

Pratyekabuddhas feel that this cycle is a lot of suffering, so they practice the Path in order to liberate themselves from birth and death. When they succeed, they attain to the fruition and become Pratyekabuddhas or Solitary Enlightened Ones, who belong to the Two Vehicles.

The Two Vehicles consist of the Hearers and Those Enlightened to Conditions (also called Solitary Enlightened Ones). The term “vehicle” is used to designate a class of cultivators. The practice of the Two Vehicles is not ultimate, because they have ended only physical birth and death, not the birth and death of thoughts. This is why Medicine Master Buddha vowed to lead the cultivators of the Lesser Vehicle to abide in the Great Vehicle and to resolve their minds on realizing the Buddhas’ Unsurpassed Enlightenment.