Bg 18.72

kaccid etac chrutam partha
tvayaikagrena cetasa
kaccid ajnana-sammohah
pranastas te dhanan-jaya

Word for word: 
kaccit — whether; etat — this; srutam — heard; partha — O son of Prtha; tvaya — by you; eka-agrena — with full attention; cetasa — by the mind; kaccit — whether; ajnana — of ignorance; sammohah — the illusion; pranastah — dispelled; te — of you; dhanam-jaya — O conqueror of wealth (Arjuna).

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O son of Prtha, O conqueror of wealth, have you heard this with an attentive mind? And are your ignorance and illusions now dispelled?

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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-gita in its proper perspective. If not, the Lord was ready to re-explain any point, or the whole Bhagavad-gita if so required. Actually, anyone who hears Bhagavad-gita from a bona fide spiritual master like Krishna or His representative will find that all his ignorance is dispelled. Bhagavad-gita 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 Krishna or from His bona fide spiritual representative is sure to become a liberated person and get out of the darkness of ignorance.