In plain words
Wherever this "I" is, this heart is there, all of it in the principle called "aham". So the heart is not in the body alone. It fills the whole world.
That has hands and feet everywhere, eyes, heads and faces everywhere; with ears everywhere in the world, It abides, enveloping all.
Wherever you look, in whatever land, in whatever age, no person whatever can be without this heart. In this heart, the sound "I" is the name of the Ātma. Therefore in every body the "I" stands as the Ātma. It is joined with Buddhi.
What Is Buddhi?
When people inquire specially what this Buddhi is, whether educated or uneducated, foolish or gifted with intelligence, they call this Buddhi the power of inquiry. They have said that discerning the eternal from the ephemeral is itself the form of Buddhi. This is not the right answer. This is not a fitting name for Buddhi. People use it merely in the world of Prakṛti, in the language of Prakṛti. But we must describe the right meaning of Buddhi well. This Buddhi has five aspects. What are these five aspects? Śraddhā, Ṛta, Satya, Yoga, Mahat-tattva. Buddhi is made up of these five aspects. How much it belittles Buddhi, joined with these five principles, to call it merely the power of discerning the eternal from the ephemeral! This Buddhi has two kinds of power. It is joined with deep faith. This faith is joined with steadiness. So, slow and steady. The very first, joined with the power of these two, is śraddhā. After this śraddhā comes Ṛta. Ṛta means this: the form that has arisen from Ṛta, joined with the purity of thought, word and deed, is itself Satya. This is what has come in the form of speech. After this Satya comes Yoga. What is this Yoga? ‘Yogaṃ cittavṛtti nirodhakaḥ.’