Chapter VI Sloka 21

suomaTyiNtk< yÄdœ buiÏ¢aýmtIiNÔym!,
veiÄ yÇ n cEvay< iSwtílit tÅvt>.

sukham˜tyantikaÕ yattad
buddhigr˜hyamateendriyam |
vetti yatra na caiv˜yaÕ 
sthitaþcalati tattvata× ( 6|21)||

When he (the Yogi) feels that infinite Bliss which can be grasped by the (pure) intellect and which transcends the senses, and established wherein he never moves from the Reality, .......
Commentary: The Infinite Bliss of the Self (which is beyond the reach of the senses) can be grasped (realised) by the pure intellect independently of the senses. During deep meditation the senses cease to function, as they are involved into their cause, the mind. The intellect is rendered pure by the practice of Yama (self-restraint) and Niyama (observances and disciplinary practices) and constant meditation.

Intellect that is purified of its rajoguna and tamoguna is called in Vedanta "the pure intellect". Tamas and Rajas create in us the 'veiling of Truth' (avarana) and the consequent agitations (vikshepana). When both of them are to a degree removed, to that extent the percentage of sattva increases in the intellect, and it is called the pure intellect. When an intellect comes under the influence of pure sattwa, it ends in an experience of infinite tranquility which is the nature of the Self, and the Self is experienced on thus transcending the intellect.