Yōga Sūtra 2.41

सत्त्वशुद्धिसौमनस्यैकाग्र्येन्द्रियजयात्मदर्शनयोग्यत्वानि च।

sattvaśuddhisaumanasyaikāgryēndriyajayātmadarśanayōgyatvāni ca।

[सत्त्व शुद्धि सौमनस्य एकाग्र्य इन्द्रिय जयः अत्म दर्शन योग्यत्वानि च।
sattva = the mode of goodness (one of the three qualities); śuddhi = purification; saumanasya = cheerful mindset; ēkāgrya = single pointed focus; indriya = senses; jayaḥ = victory over; atma = self; darśana = directly perceive; yōgyatvāni = based on one's ability; ca = and;]

Through purification, when saatwik quality and cheerful mind set is established, one gains single pointed focus, victory over senses, and the ability to directly perceive the self.