Master Hsuan Hua offers this explanation of the Bodhisattva’s Four Great Vows in his discussion of Chapter 3, A Parable, in the Lotus Sutra and the description of the characteristics of the Great Cart given to the children who escape the Burning House of the Triple World.

The first of the four vast vows is, “Living beings are boundless; I vow to save them all.” The beings in our inherent nature are countless and limitless. You must first save beings within yourself before you can save beings on the outside. If you have not finished saving the beings within yourself, you cannot finish saving living beings on the outside. Although you have saved living beings, you should not become attached to having done so. You should save all living beings yet have no attachment to having saved them.

The second of the four vast vows is, “Afflictions are endless; I vow to cut them off.” Our afflictions arise without our intending to produce them. We try to avoid having afflictions, yet afflictions still arise. Without realizing how it happens, ignorance manifests. The Heart Sutra discusses twenty types of subsidiary afflictions. Without cause or reason, afflictions arise. One vows to sever these afflictions, but they continue to arise. We would be well-off indeed if we had as much money as we had afflictions. Then we’d always have money – no need to work for it. It’s too bad we don’t have as much money as we do afflictions. Afflictions are never-ending. Money is not. Once you use it, it’s gone. But there are people who think afflictions are the best thing. They get angry and think it’s more fun than eating dumplings. Is this strange or not? Giving rise to afflictions will burn away one’s virtues and Dharma wealth. That is why the Buddha taught all living beings to sever afflictions. Afflictions must be cut off.

The third vow Is, “Dharma-doors are countless; I vow to study them all.” Last year you studied the Śūraṅgama Sūtra. This year you are studying the Dharma Flower Sūtra, the Heart Sūtra, the Vajra Sūtra, and the Earth Store Sūtra; and soon we will have lectures on the Avataṃsaka Sūtra as well. Each sūtra has its own principles. How many doctrines would you say there are? There are as many as the grains of sand in the Ganges, as many as motes of dust. The Avataṃsaka Sūtra in its original form has as many chapters as the motes of dust in ten trichiliocosms. How many is that? It is as many as those dust motes. If you can count how many dust motes there are, then you know how many chapters there are. If you can’t, don’t ask me, because I am just like you.

As to Dharma-doors, there are the Great Vehicle Dharmas, the Lesser Vehicle Dharmas, the four noble truths, the six pāramitās, the twelve links of dependent arising, the thirty-seven factors of awakening… How many Dharmas are there? There are 84,000 Dharma-doors. If we were to study one Dharma-door every day, we would need 84,000 days. How many days are there in our lives? There are 365 days in a year, 3,650 days in ten years, and 36,500 days in one hundred years – so we would be dead before we finished studying. National Master Qingliang lived to be 101. How can we ever finish learning all wisdom and knowledge? We can never finish learning. If not, should we quit studying? No. Even though we cannot finish studying, we still need to study. “Dharma-doors are countless; I vow to study them all.” If we do not study, we will not learn. So we must keep studying. …

The fourth vow Is, “Buddhahood is unsurpassed; I vow to realize it.” In this world, there is nothing higher than the realization of Buddhahood. Becoming a Buddha is the most honorable accomplishment both in and beyond this world. Therefore, the Buddha, the World Honored One, is the most honored both within and beyond the world. Buddhahood is the ultimate refuge and final accomplishment. Before becoming a Buddha, one is simply a confused being in the nine Dharma realms. After becoming a Buddha, one is completely clear, without any confusion. This is why we vow, “Buddhahood is unsurpassed; I vow to realize it.” We vow to become Buddhas. Not only will we become Buddhas, we will lead all living beings to realize Buddhahood together.

These four vast vows are truly magnificent. “I vow to save the living beings of my inherent nature. I vow to cut off the afflictions of my inherent nature.” You can’t just run around telling other people that they should cut off their afflictions. You can’t walk up to someone and say, “You are studying the Buddhadharma, yet you still have so many afflictions. You still have a terrible temper. Just what meaning does all your study have?” You are not supposed to be looking at others’ faults. You are supposed to watch over yourself….

The four vast vows are very important. They are represented in the text by the phrase “with golden cords strung around them.” The four vast vows are like cords of gold braided together. You have to be vigorous. Don’t ever forget these vows. Always base your cultivation upon these four vast vows.

These vows, which are know in Nichiren Shu Buddhism as the Four Great Vows, are derived from T’ien T’ai Buddhism. There’s an excellent discussion of how these vows are derived from the Four Noble Truths in a 1983 article by Robert F. Rhodes. (PDF)