Shvetashvatara Upanishad 5.8
intermediate
अङ्गुष्ठमात्रो रविनुल्यरूपः संकल्पाहङ्कारसमन्वितो यः। बुद्धेर्गुणेनात्मगुणेन चैव आराग्रमात्रो ह्यपरोऽपि दृष्टः॥
aṅguṣṭhamātro ravinulyarūpaḥ saṃkalpāhaṅkārasamanvito yaḥ | buddheguṇenātmaguṇena caiva ārāgramātro hyaparo\'pi dṛṣṭaḥ ||
"Thumb-sized, like the sun in appearance, endowed with will and ego, with the quality of intellect and the quality of the self - this other one is seen as small as the tip of a goad."
What This Means:
The Self is described as thumb-sized, like a sun, having will, ego, and intellect. It is seen as tiny as a goad's point.
Going Deeper:
The "thumb-sized" Self in the heart is a recurring Upanishadic image (Katha 6.17). Though luminous like the sun, it appears tiny because of limiting adjuncts.
How To Apply This:
Meditate on the luminous Self in the heart, thumb-sized, radiant as the sun.
#thumb-sized Self#heart#luminous#ego#intellect