तत्क्षेत्रं यच्च यादृक् च यद्विकारि यतश्च यत्। स च यो यत्प्रभावश्च तत्समासेन मे श्रृणु ॥

tat kṣhetraṁ yach cha yādṛik cha yad-vikāri yataśh cha yat sa cha yo yat-prabhāvaśh cha tat samāsena me śhṛiṇu

What that Field is and of what nature, how modified, and whence it is, and what He is and what His powers, hear that now briefly from Me.

In plain words: Krishna says he will now briefly explain what the Field, the body and world, is like, how it changes and where it comes from. He will also explain who the Knower is and what powers he has.