The rishis of Rig Veda clearly understood that the perceiving capacity of all humans is not equal

Rigveda 1.164.45 establishes that speech operates on four levels, while Rigveda 10.71.7 illustrates how human capabilities diverge when processing these deeper, intuitive levels of language and thought

a)          The Four Levels of Speech (Rigveda 1.164.45) 

चत्वारि वाक्परिमिता पदानि तानि विदुर्ब्राह्मणा ये मनीषिणः ।

गुहा त्रीणि निहिता नेङ्गयन्ति तुरीयं वाचो मनुष्या वदन्ति ॥

 catvāri vāk parimitā padāni tāni vidur brāhmaṇā ye manīṣiṇaḥ |

guhā trīṇi nihitā neṅgayanti turīyaṃ vāco manuṣyā vadanti || 

English translation:

Speech is measured in four feet. Rishis of inspired thinking (manīṣiṇaḥ) know these. They do not set in motion the three that are imprinted in secret (guhā); the sons of Manu speak the fourth (foot/quarter) of speech.

The Spoken One: Ordinary humans speak only the fourth, outermost part (turīyaṃ vāco). 

Later Classifications: In later Vedic and Tantric literature (such as the Upanishads and Bhartrihari's Vakyapadiya), these four levels were formally named:

1. Parā: Transcendent, unmanifest sound.
2. Paśyantī: Visualized, intuitive thought-speech.
3. Madhyamā: Mental intermediate speech.
4. Vaikharī: Articulated, physical speech (the turīya spoken by ordinary people). 

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b)              The Human Divergence

Rigveda 10.71 is a hymn dedicated entirely to Jñānam (Knowledge) and Vāk (Speech). Mantra 7 highlights that even though humans possess identical sensory organs, their internal perceiving capacities differ heavily:

Rigveda 10.71.7

अक्षण्वन्तः कर्णवन्तः सखायो मनोजवेष्वसमा बभूवुः ।

आदघ्नास उपकक्षास उ त्वे ह्रदा इव स्नात्वा उ त्वे ददृश्रे ॥

akṣaṇvantaḥ karṇavantaḥ sakhāyo manojaveṣv asamā babhūvuḥ |

ādaghnāsa upakakṣāsa u tve hradā iva snātvā u tve dadṛśre ||

English translation:

Though all have eyes and ears, the companions are unequal in quickness of mind. Some seem like ponds reaching up to the mouth or up to the armpits, and others seem like ponds good to bathe in.”

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Literally, "Spiritual practitioners, who possess eyes (akṣaṇvantaḥ) and ears (karṇavantaḥ) prove to be unequal in the quickness of their minds’ perceiving capacity (manojaveṣv asamā babhūvuḥ).

The same Rik uses a metaphor of people entering a body of water. For some, the water reaches only up to their mouths (ādaghnāsa); for others, to their armpits (upakakṣāsa); while some are deep enough to bathe completely (snātvā).

Every human can easily speak and hear physical speech (Vaikharī / Turīya). However, diving into the mental and unmanifest origins of Divine language requires internal mental Intuitive velocity and depth (manojava).

The Rishis are those whose mental pools are deep. They can plunge past superficial speech into the unmoving, hidden levels (guhā trīṇi). Ordinary people remain on the surface, unequal to the seers because their cognitive velocity is restricted to external stimuli.