In the part of the Katha-Upanishad which intervenes between the passage
'The Person of the size of a thumb stands in the middle of the Self (II,
4, 12), and the passage 'The Person of the size of a thumb, the inner
Self' (II, 6, 17), we meet with the text 'whatever there is, the whole
world, when gone forth, trembles in its breath. A great terror, a raised
thunderbolt; those who knew it became immortal. From fear of it fire
burns, from fear the sun shines, from fear Indra and Vâyu, and Death as
the fifth run away' (II, 6, 2; 3). This text declares that the whole
world and Agni, Sûrya, and so on, abiding within that Person of the size
of a thumb, who is here designated by the term 'breath,' and going forth
from him, tremble from their great fear of him. 'What will happen to us
if we transgress his commandments?'--thinking thus the whole world
trembles on account of great fear, as if it were a raised thunderbolt.
In this explanation we take the clause 'A great fear, a raised
thunderbolt,' in the sense of '(the world trembles) from great fear,' &c.,
as it is clearly connected in meaning with the following clause: 'from
fear the fire burns,' &c.--Now what is described here is the nature of
the highest Brahman; for that such power belongs to Brahman only we know
from other texts, viz.: 'By the command of that Imperishable, O Gârgî,
sun and moon stand apart' (Bri. Up. III, 8, 9); and 'From fear of it the
wind blows, from fear the sun rises; from fear of it Agni and Indra, yea
Death runs as the fifth' (Taitt. Up. II, 8, 1).--The next Sûtra supplies
a further reason.