BG Chap 8 - The process by which yogi attains the Lord
One who at the time of death, fixes his life air between the eyebrows and with an undeviating mind engages himself in remembering the Lord, attains that Supreme Person. He attains an unwavering mind thru the strength of yoga practice. He who remembers with undeviating mind that person at the time of death, with prema for Paramātmā (bhaktyā), thru the accumulation of impressions arising from the experience of samādhi, carefully establishing the life air between the eyebrows, attains the Lord. A pure devotee does not practice such yoga, but because he is always engaged in Kṛṣṇa consciousness, at death he can remember the Supreme Personality of Godhead by His grace.
The knowers of the Vedas say that the syllable oṁ represents the indestructible Brahman. The sannyāsīs, who have given up ignorance, attain that Brahman indicated by the sound oṁ. The students of Brahman, desiring to know this Brahman and its form as oṁ, follow vows of celibacy.