Bg 6.45

prayatnād yatamānas tu
yogī saṁśuddha-kilbiṣaḥ
aneka-janma-saṁsiddhas
tato yāti parāṁ gatim
Synonyms: 
prayatnāt — by rigid practice; yatamānaḥ — endeavoring; tu — and; yogī — such a transcendentalist; saṁśuddha — washed off; kilbiṣaḥ — all of whose sins; aneka — after many, many; janma — births; saṁsiddhaḥ — having achieved perfection; tataḥ — thereafter; yāti — attains; parām — the highest; gatim — destination.
Translation: 
And when the yogī engages himself with sincere endeavor in making further progress, being washed of all contaminations, then ultimately, achieving perfection after many, many births of practice, he attains the supreme goal.
Purport: 

A person born in a particularly righteous, aristocratic or sacred family becomes conscious of his favorable condition for executing yoga practice. With determination, therefore, he begins his unfinished task, and thus he completely cleanses himself of all material contaminations. When he is finally free from all contaminations, he attains the supreme perfection – Kṛṣṇa consciousness. Kṛṣṇa consciousness is the perfect stage of being freed of all contaminations. This is confirmed in the Bhagavad-gītā (7.28):

yeṣāṁ tv anta-gataṁ pāpaṁ
janānāṁ puṇya-karmaṇām
te dvandva-moha-nirmuktā
bhajante māṁ dṛḍha-vratāḥ

“After many, many births of executing pious activities, when one is completely freed from all contaminations, and from all illusory dualities, one becomes engaged in the transcendental loving service of the Lord.”