Here the Lord informs Arjuna that this system of yoga, the Bhagavad-gītā, was first spoken to the sun-god, and the sun-god explained it to Manu, and Manu explained it to Ikṣvāku, and in that way, by disciplic succession, one speaker after another, this yoga system has been coming down. But in the course of time it has become lost. Consequently the Lord has to speak it again, this time to Arjuna on the Battlefield of Kurukṣetra.
He tells Arjuna that He is relating this supreme secret to him because Arjuna is His devotee and His friend. The purport of this is that Bhagavad-gītā is a treatise which is especially meant for the devotee of the Lord. There are three classes of transcendentalists, namely the jñānī, the yogī and the bhakta, or the impersonalist, the meditator and the devotee. Here the Lord clearly tells Arjuna that He is making him the first receiver of a new paramparā (disciplic succession) because the old succession was broken. It was the Lord's wish, therefore, to establish another paramparā in the same line of thought that was coming down from the sun-god to others, and it was His wish that His teaching be distributed anew by Arjuna.