Taittirīyopaniṣat 02.16

यदा ह्येवैष एतस्मिन्नदृश्ये अनात्म्ये अनिरुक्ते अनिलयने अभयं प्रतिष्ठां विन्दते। अथ सोऽभयं गतो भवति। यदा ह्येवैष एतस्मिन्नुदरमन्तरं कुरुते। अथ तस्य भयं भवति। तत्त्वेव भयं विदुषोऽमन्वानस्य॥

When one finds the foundation of fearlessness in that which is unseen, that 'anātmya', undefined, and without abode, then he attains fearlessness. But when one creates distinction within this (i.e he is independent from this essence), then fear arises for him. That indeed is truly fear for the knower who perceives difference.

तदप्येष श्लोको भवति। भीषास्माद् वातः पवते। भीषोदेति सूर्यः। भीषाऽस्मादग्निश्चेन्द्रश्च। मृत्युर्धावति पञ्चम इति ॥१६॥

There is also this verse: "From fear of Him the wind blows, from fear the sun rises, from fear of Him fire and Indra, and Death as the fifth, run their courses."

Taittirīya Bhāshya 02.16

The Lord is said to be 'anātma', as He is different from the individual beings in terms of attributes. The supreme Viṣṇu alone is described as 'ā', as is higher than all other principles and beings. He is infinite in qualities, unexpressed and without dependence. An individual being begets fear when he thinks he is independent of Lord Vishnu. Liberated beings, such as the wise Vāyu and others, who governs the universe, are fearless because they always perform their duties directly to please Lord Viṣṇu.

"तस्माददृश्ये जैवानां गुणानामप्यसङ्गतेः। अनात्म्येऽथ गुणानन्त्यादनिरुक्ते निराश्रयात्॥ अनिलयनेऽभयत्वेन यदा ज्ञानेन तिष्ठति। तदाऽभयं हरिं गच्छेन्नैवाज्ञानी कथञ्चन॥

"Therefore, that which is unseen and not associated even with the limited qualities of living beings is termed as 'anātma', i.e. not the individual being; He is infinite in qualities, unexpressed and without support. One attains Hari (the Supreme) when one is not dependent on any abode, is in a state of fearlessness and remains in knowledge; but the ignorant never attains Him in any way.

यदैतस्मिन् परे विष्णावुदरं जीवगत्वतः। भेदं करोति तेनैव भयमस्य महद् भवेत्॥

If one creates division in this Supreme Lord Viṣṇu, the origin of all living beings, then from that very act, great fear arises for him.

आ इत्युक्तः परो विष्णुरेभ्य उच्च स एव तु। त उदा जीवसङ्घाः स्युरुदरं तद्गतान्तरम्॥ तदेव ब्रह्म भयकृद् विदुषोऽविदुषस्तथा। विदुषोऽल्पभयं कुर्याद् यावन्मुक्तिं व्रजत्यसौ॥

The supreme Viṣṇu, thus described as 'ā' alone, is higher than all these. From him arise the groups of living beings, who may be within the belly, having entered there. That very Brahman is the source of fear for both the wise and the ignorant. For the wise, it causes only little fear until they attain liberation.

अथाभयं भवेद् ब्रह्म तस्य मुक्तस्य सर्वदा। तस्माद् वाय्वादयो देवा विद्वांसोऽपि विशेषतः॥

Now, for the liberated one, Brahman is always fearlessness. Especially this is so with the gods beginning with Vāyu, the wise.

भीताः स्वकर्म कुर्वन्ति विष्णोः प्रीत्यर्थमञ्जसा। अमन्वानस्य नुर्विष्णुः कुर्यान्नित्यं महद्भयम्॥ तमआख्यमनुत्थानम् .... ॥"

Out of fear, people perform their duties directly to please Lord Viṣṇu. For one who does not follow, the great Viṣṇu would always instil great fear. This is called inaction ...."