SB 3.8.22

kālena so ’jaḥ puruṣāyuṣābhi-
 pravṛtta-yogena virūḍha-bodhaḥ
svayaṁ tad antar-hṛdaye ’vabhātam
 apaśyatāpaśyata yan na pūrvam
Word for word: 
kālena — in due course of time; saḥ — he; ajaḥ — the self-born Brahmā; puruṣa-āyuṣā — by the duration of his age; abhipravṛtta — being engaged; yogena — in meditation; virūḍha — developed; bodhaḥ — intelligence; svayam — automatically; tat antaḥ-hṛdaye — in the heart; avabhātam — manifested; apaśyata — saw; apaśyata — did see; yat — which; na — not; pūrvam — before.
Translation: 
At the end of Brahmā’s one hundred years, when his meditation was complete, he developed the required knowledge, and as a result he could see in his heart the Supreme within himself, whom he could not see before with the greatest endeavor.
Purport: 

The Supreme Lord can be experienced only through the process of devotional service and not by one’s personal endeavor in mental speculation. The age of Brahmā is calculated in terms of divya years, which are distinct from the solar years of human beings. The divya years are calculated in Bhagavad-gītā (8.17): sahasra-yuga-paryantam ahar yad brahmaṇo viduḥ. Brahmā’s one day is equal to one thousand times the aggregate of the four yugas (calculated to be 4,300,000 years). On that basis, Brahmā meditated for one hundred years before he could understand the supreme cause of all causes, and then he wrote the Brahma-saṁhitā, which is approved and recognized by Lord Caitanya and in which he sings, govindam ādi-puruṣaṁ tam ahaṁ bhajāmi. One has to wait for the mercy of the Lord before one can either render service unto Him or know Him as He is.