Verse 7.3.1

मनो वाव वाचो भूयो यथा वै द्वे वामलके द्वे वा कोले द्वौ वाक्षौ मुष्टिरनुभवत्येवं वाचं च नाम च मनोऽनुभवति स यदा मनसा मनस्यति मन्त्रानधीयीयेत्यथाधीते कर्माणि कुर्वीयेत्यथ कुरुते पुत्रांश्च पशूंश्चेच्छेयेत्यथेच्छत इमं च लोकममुं चेच्छेयेत्यथेच्छते मनो ह्यात्मा मनो हि लोको मनो हि ब्रह्म मन उपास्स्वेति ॥ ७.३.१ ॥

mano vāva vāco bhūyo yathā vai dve vāmalake dve vā kole dvau vākṣau muṣṭiranubhavatyevaṃ vācaṃ ca nāma ca mano'nubhavati sa yadā manasā manasyati mantrānadhīyīyetyathādhīte karmāṇi kurvīyetyatha kurute putrāṃśca paśūṃśceccheyetyathecchata imaṃ ca lokamamuṃ ceccheyetyathecchate mano hyātmā mano hi loko mano hi brahma mana upāssveti || 7.3.1 ||

1. The mind is superior to speech. Just as a person can hold in his fist two āmalaka fruits, or two kola fruits [plums], or two akṣa fruits, so also the mind can hold within it both speech and name. If a person thinks, ‘I will read the mantras,’ he reads them. If he thinks, ‘I will do this,’ he does it. If he decides, ‘I will have children and animals,’ he can try to have them. If he decides, ‘I will conquer this world and the next,’ he can try to do it. [This is the characteristic of the mind. If it says it will do something, it can do it.] The mind is the self. The mind is the world. The mind is Brahman. Worship the mind.

Word-for-word explanation:

Manaḥ vāva vācaḥ bhūyaḥ, the mind is certainly superior to speech; yathā vai, just as; dve vā āmalake, two āmalaka fruits; dve vā kole, or two kolas [plums]; dvau vā akṣau, or two akṣa fruits; muṣṭiḥ anubhavati, the fist can hold; evam, in the same way; manaḥ anubhavati, the mind can hold; vācam ca nāma ca, speech and mind; yadā, when; saḥ, someone; manasā, in his mind; manasyati, thinks; mantrān adhīyīya iti, I will read the mantras; atha, then; adhīte, he reads; karmāṇi kurvīya iti, I will work; atha, then; kurute, he works; putrān ca paśūn ca, children and animals; iccheya iti, let me wish for; atha icchate, then he wishes; imam ca lokam amum ca, this world and the other world; iccheya iti, let me wish for; atha icchate, then he wishes; manaḥ hi ātmā, the mind is the self; manaḥ hi lokaḥ, the mind is the world; manaḥ hi brahma, the mind is Brahman; manaḥ upāssva iti, worship the mind.

Commentary:

Speech and name are important, but they are not enough. They will not take you very far. Suppose you repeat the name of God, but your mind is elsewhere, thinking of something else. Will that serve any purpose? No.

The Upaniṣad says here, first you decide in your mind what you will do, and after that you act on the thought. Just as you hold fruits within your hand, similarly, you hold within your mind what you want—whether it is children, property, scholarship, or something else. So the mind is higher than speech.