Bhagavad Gita Chapter 14, Verse 3

मम योनिर्महद्ब्रह्म तस्मिन्गर्भं दधाम्यहम् | सम्भवः सर्वभूतानां ततो भवति भारत ||

mama yonir mahad brahma tasmin garbhaṁ dadhāmy aham sambhavaḥ sarvabhūtānāṁ tato bhavati bhārata

My womb is the great Brahman (material nature). In that I place the seed. From that comes the birth of all beings, O Arjuna.

Krishna explains how material nature works: 'Mama yonir mahad brahma'—My womb is the great Brahman (material nature/prakriti). 'Tasmin garbhaṁ dadhāmi aham'—in that I place the seed. This is the process of creation: Krishna (the Supreme) places the seed (the living entities/souls) into material nature (prakriti). 'Sambhavaḥ sarvabhūtānāṁ tato bhavati'—from that comes the birth of all beings. This verse reveals the relationship between the Supreme and material nature. Krishna is the source—He places the seed (souls) into material nature, and material nature, with its three gunas, creates all the forms of life. Understanding this helps you see that material nature is not independent—it's an instrument of the Supreme. The gunas are qualities of material nature, and they influence everything that comes from it. This sets up the next verses, which will explain how the three gunas manifest.