The Medicine Buddha Sutra, or more fully, the Sutra of the Merits of the Original Vows of Medicine Master Crystal Light Tathagata, is a Great Vehicle sutra that praises the vow and the actions of Medicine Buddha.
The Medicine Buddha, also known as Medicine Master Crystal Light Tathagata, is the founding teacher in the Land of Pure Crystal Light, which is the pure land of the east. The word "crystal" in the name uses the brilliance and clarity of crystal as an analogy for how this land is completely pure and without defilements.
In the past, for many kalpas, the Medicine Buddha engaged in purifying practices. When Lightening Buddha was in this world, He made 12 great vows, including the vows to eliminate the sufferings of illness sentient beings face, to help all sentient beings be born with all their faculties intact, with magnificent bodily appearances, to give them abundant tools and resources, to help them be free of all suffering and to guide them to reach liberation.
Sentient beings have many afflictions from their bodies and minds. In particular, Three Poisons of greed, anger and doubt can produce 84,000 different kinds of afflictions. The minds of sentient beings are full of suffering, which can lead to 440 different kinds of physiological illnesses, thus causing both body and mind to be tormented.
The Medicine Buddha vowed to help sentient beings eliminate these afflictions and avoid the illnesses that bind their bodies, reduce their pain and suffering, and be liberated from disasters.
In 1966, when the Buddhist Tzu Chi Merit Association was established, every 24th of the month on the lunar calendar was a day that Tzu Chi would hold distributions. At that time, this was referred to as the "Tzu Chi Dharma Assembly." Later, out of gratitude for those who had formed the aspiration to donate small amounts through the bamboo banks, Master Cheng Yen broke her own rule of not holding repentance ceremonies or sutra recitations, and made a vow that the Medicine Buddha Sutra would be chanted monthly at the abode during the distribution. This was to encourage everyone to keep in mind the 12 great vows of Medicine Buddha and constantly actualize the practice of saving oneself and others. The name of this event was later changed to the "Medicine Buddha Sutra Dharma Assembly." This is the affinity between Tzu Chi and the Medicine Buddha Sutra.
In modern era, those who know the names of different medicines and prescribe them accordingly are called "pharmacists" (literally medicine masters in Chinese). In the Buddha's era, not only could the Buddha prescribe the right medicine for the disease, He could also see clearly into the imbalance of the four elements in the world and analyze the psychological illnesses that people had. So, He is respectfully called the Great Medicine King, or the Great Healer. In fact, the medicine He gave was the Dharma; if we know how to apply them, then all things in the world are beneficial medicines.
Master Cheng Yen gave this series of lectures on the Medicine Buddha Sutra from July, 2001 to July 2002, at the beginning of 21st century. As she observed that standards of morality and propriety were not being followed and interpersonal relationships were filled with conflict and opposition, she began teaching on the Medicine Buddha Sutra during her morning Dharma talks, hoping to start the process of healing.
Master Cheng Yen humbly reads the sutra text and explains its meaning sentence by sentence, enabling the listener to eventually have an overall understanding of the sutra. There is no doubt that this is her unique way to heal the illnesses that are prevalent in the modern world and reach her goal of bringing peace and harmony. Thus, her teachings focus on promoting the cultivation of virtue as the medicine prescribed to heal the world.