Verse 3.14.3

एष म आत्मान्तर्हृदयेऽणीयान्व्रीहेर्वा यवाद्वा सर्षपाद्वा श्यामाकाद्वा श्यामाकतण्डुलाद्वैष म आत्मान्तर्हृदये ज्यायान्पृथिव्या ज्यायानन्तरिक्षाज्ज्यायान्दिवो ज्यायानेभ्यो लोकेभ्यः ॥ ३.१४.३ ॥

eṣa ma ātmāntarhṛdaye'ṇīyānvrīhervā yavādvā sarṣapādvā śyāmākādvā śyāmākataṇḍulādvaiṣa ma ātmāntarhṛdaye jyāyānpṛthivyā jyāyānantarikṣājjyāyāndivo jyāyānebhyo lokebhyaḥ || 3.14.3 ||

3. My Self within my heart is smaller than a grain of rice, smaller than a grain of barley, smaller than a mustard seed, smaller than a grain of millet, smaller even than the kernel of a grain of millet. The Self in my heart is larger than the earth, larger than the mid-region, larger than heaven, and larger even than all these worlds.

Word-for-word explanation:

Eṣaḥ me ātmā, this my Self; antaḥ hṛdaye, inside the heart; aṇīyān, smaller than; vrīheḥ vā, a grain of rice; yavāt vā, or a grain of barley; sarṣapāt vā, or a mustard seed; śyāmākāt vā, or a grain of millet; śyāmākataṇḍulāt vā, or the kernel of a grain of millet; eṣaḥ me ātmā antaḥ hṛdaye, this Self within my heart; jyāyān pṛthivyā, is larger than the earth; jyāyān antarikṣāt, larger than the mid-region; jyāyān divaḥ, larger than heaven; jyāyān ebhyaḥ lokebhyāḥ, larger than all these worlds.

Commentary:

The underlying idea in the verse is that the Self is everything and everywhere. It is therefore smaller than the smallest and bigger than the biggest.