From the Law of Dependent Origination, the Source of All Dharmas Can Be Inferred.

In worldly affairs there is a saying: the growth of all things cannot be separated from the sun. If all things depend on the sun in order to exist, then what does the sun itself depend on for its existence? If you trace back thing by thing, eventually you will reach a point where you can trace no further; at that point you can deduce something most ultimate—something that exists on its own without depending on other conditions or other dharmas. This thing need not be born and never perishes, and therefore it is the most reliable, the most dependable.

When the pratyekabuddhas traced the dharma of causes and conditions, they finally traced it to the Ālayavijñāna and could trace no further, so they arrived at a conclusion: consciousness conditions name-and-form, and name-and-form condition consciousness. In this way the source of all dharmas was traced out, and that is the Ālayavijñāna. The name-and-form of the five aggregates are directly born from the Ālayavijñāna, while all other dharmas are merely contributing conditions for their arising; the birth of all things is likewise so. When we study Buddhism and cultivate practice, we must also learn to reason in this way; then many dharmas can be realized by ourselves without needing others to teach us, and seeing the mind and realizing the tathāgatagarbha is not really so difficult.

The Śūraṅgama Sūtra says that sunlight does not come from the sun but comes directly from within the tathāgatagarbha. By the same reasoning, the growth of all things does not rely on the sun but on the tathāgatagarbha: it is the tathāgatagarbha that transmits the seeds of the four great elements, causing all things to grow. If the tathāgatagarbha did not transmit the seeds of the four great elements, no matter how the sunlight shone, all things could not grow—on the contrary, they would die. Moreover, sunlight itself is formed by the tathāgatagarbha transmitting the seeds of the four great elements, and not for even a single instant has it ever departed from the tathāgatagarbha.

If you study the Śūraṅgama Sūtra well, your thinking will become broad and clear, and you will know that the arising, existence, and operation of all dharmas are the nature of the tathāgatagarbha, and not anything else. For one thing to give birth to another thing—that is impossible. Because this thing is without self-nature, subject to arising and ceasing, not enduring forever, how could it give birth to another thing? All things are born directly from the tathāgatagarbha; other things are merely contributing conditions. A thing cannot produce other things—things do not produce things; all dharmas are created by the mind alone. When all dharmas are traced to the end, to the point where they can be traced no further, there is nothing left to return to; that which cannot be returned to is the tathāgatagarbha.