aham ajnana-jam tamah
Word for word:
tesam — for them; eva — certainly; anukampa-artham — to show special mercy; aham — I; ajnana-jam — due to ignorance; tamah — darkness; nasayami — dispel; atma-bhava — within their hearts; sthah — situated; jnana — of knowledge; dipena — with the lamp; bhasvata — glowing.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
To show them special mercy, I, dwelling in their hearts, destroy with the shining lamp of knowledge the darkness born of ignorance.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When Lord Caitanya was in Benares promulgating the chanting of Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare, thousands of people were following Him. Prakasananda Sarasvati, a very inﬂuential and learned scholar in Benares at that time, derided Lord Caitanya for being a sentimentalist. Sometimes Mayavadi philosophers criticize the devotees because they think that most of the devotees are in the darkness of ignorance and are philosophically naive sentimentalists. Actually that is not the fact. There are very, very learned scholars who have put forward the philosophy of devotion. But even if a devotee does not take advantage of their literatures or of his spiritual master, if he is sincere in his devotional service he is helped by Krishna Himself within his heart. So the sincere devotee engaged in Krishna consciousness cannot be without knowledge. The only qualiﬁcation is that one carry out devotional service in full Krishna consciousness.
The Mayavadi philosophers think that without discriminating one cannot have pure knowledge. For them this answer is given by the Supreme Lord: those who are engaged in pure devotional service, even though they be without sufﬁcient education and even without sufﬁcient knowledge of the Vedic principles, are still helped by the Supreme God, as stated in this verse.
The Lord tells Arjuna that basically there is no possibility of understanding the Supreme Truth, the Absolute Truth, the Supreme Personality of Godhead, simply by speculating, for the Supreme Truth is so great that it is not possible to understand Him or to achieve Him simply by making a mental effort. Man can go on speculating for several millions of years, and if he is not devoted, if he is not a lover of the Supreme Truth, he will never understand Krishna, or the Supreme Truth. Only by devotional service is the Supreme Truth, Krishna, pleased, and by His inconceivable energy He can reveal Himself to the heart of the pure devotee. The pure devotee always has Krishna within his heart; and with the presence of Krishna, who is just like the sun, the darkness of ignorance is at once dissipated. This is the special mercy rendered to the pure devotee by Krishna.
Due to the contamination of material association, through many, many millions of births, one’s heart is always covered with the dust of materialism, but when one engages in devotional service and constantly chants Hare Krishna, the dust quickly clears, and one is elevated to the platform of pure knowledge. The ultimate goal, Visnu, can be attained only by this chant and by devotional service, and not by mental speculation or argument. The pure devotee does not have to worry about the material necessities of life; he need not be anxious, because when he removes the darkness from his heart, everything is provided automatically by the Supreme Lord, who is pleased by the loving devotional service of the devotee. This is the essence of the teachings of Bhagavad-gita. By studying Bhagavad-gita, one can become a soul completely surrendered to the Supreme Lord and engage himself in pure devotional service. As the Lord takes charge, one becomes completely free from all kinds of materialistic endeavors.