Bg 18.72

kaccid etac chrutaṁ pārtha
tvayaikāgreṇa cetasā
kaccid ajñāna-sammohaḥ
praṇaṣṭas te dhanañ-jaya
Word for word: 
kaccit — whether; etat — this; śrutam — heard; pārtha — O son of Pṛthā; tvayā — by you; eka-agreṇa — with full attention; cetasā — by the mind; kaccit — whether; ajñāna — of ignorance; sammohaḥ — the illusion; praṇaṣṭaḥ — dispelled; te — of you; dhanam-jaya — O conqueror of wealth (Arjuna).
Translation: 
O son of Pṛthā, O conqueror of wealth, have you heard this with an attentive mind? And are your ignorance and illusions now dispelled?
Purport: 

The Lord was acting as the spiritual master of Arjuna. Therefore it was His duty to inquire from Arjuna whether he understood the whole Bhagavad-gītā in its proper perspective. If not, the Lord was ready to re-explain any point, or the whole Bhagavad-gītā if so required. Actually, anyone who hears Bhagavad-gītā from a bona fide spiritual master like Kṛṣṇa or His representative will find that all his ignorance is dispelled. Bhagavad-gītā is not an ordinary book written by a poet or fiction writer; it is spoken by the Supreme Personality of Godhead. Any person fortunate enough to hear these teachings from Kṛṣṇa or from His bona fide spiritual representative is sure to become a liberated person and get out of the darkness of ignorance.