Verse 4

एकत्वे विद्यमानस्य सर्वगस्य किलात्मनः ।अयं बन्धुः परश्चायमित्यसौ कलना कुतः

In plain words

For the ātman, which truly exists as one, all-pervading -- where, indeed, does this very notion come from, 'this one is kin, and this one is other'?