Questions and answers among different classes of men have different value. Inquiries by mercantile men in a business exchange cannot be expected to be highly purposeful in spiritual values. Questions and answers by different classes of men can be guessed by the caliber of the persons concerned. In Bhagavad-gītā, the discussion was between Lord Śrī Kṛṣṇa and Arjuna, the Supreme Person and the supreme devotee respectively. The Lord admitted Arjuna to be His devotee and friend (BG 4.3), and therefore any sane man can guess that the discussion was on the topic of the bhakti-yoga system. Actually the whole Bhagavad-gītā is based on the principle of bhakti-yoga. There is a difference between karma and karma-yoga. Karma is regulated action for the enjoyment of the fruit by the performer, but karma-yoga is action performed by the devotee for the satisfaction of the Lord. Karma-yoga is based on bhakti, or pleasing the Lord, whereas karma is based on pleasing the senses of the performer himself. According to Śrīmad-Bhāgavatam, one is advised to approach a bona fide spiritual master when one is actually inclined to question from an elevated level of spiritual understanding. A common man who has no interest in spiritual values has no need to approach a spiritual master just as a matter of following fashion.
As a student, Mahārāja Parīkṣit was serious about learning the science of God, and Śukadeva Gosvāmī was a bona fide spiritual master in the transcendental science. Both of them knew that the topics discussed by Vidura and Ṛṣi Maitreya were elevated, and thus Mahārāja Parīkṣit was very interested in learning from the bona fide spiritual master.