Bhagavad Gita 18.72कच्चिदेतच्छ्रुतं पार्थ त्वयैकाग्रेण चेतसा।कच्चिदज्ञानसंमोहः प्रनष्टस्ते धनञ्जय ॥

It is the duty of the spiritual teacher or preceptor to make the aspirant understand the teaching of the scripture and to enable him to attain the goal of life (Moksha). If the student has not grasped the subject he will have to explain it in some other way with similes, analogies and illustrations. That is the reason why Lord Krishna asks Arjuna Has the delusion of thy ignorance been destroyedThis What I have told thee.Have you heard it, O Arjuna, with onepointed mind Have you grasped My teachingDelusion of ignorance The absence of discrimination which is caused by ignorance and which is natural. The destruction of delusion is the aim of all this endeavour on your part to hear the scripture and the exertion on My part as the teacher.