Bhagavad Gita · Jnana Karma Sannyasa YogaChapter 4, Shloka 3 (4.3)

Two qualifications — devotion and friendship. The right to this knowledge comes not from Arjuna's intellect or position, but from his love and friendship.

Shankaracharya: bhakto 'si me sakhā ca asi iti — because you are a devotee and a friend; rahasyaṃ hi yasmāt etat uttamaṃ yogaḥ jñānam — for this is the supreme secret, namely yoga — knowledge. At the end of 4.3 Shankara says that Arjuna's next question (4.4) is codyam iva — like an objection — so that no one should think the Lord has said something contradictory.

Acharya Ramanuja: sa eva ayam askhalita-svarūpaḥ purātanaḥ yogaḥ — this is that same ancient yoga, unshaken in its nature; sakhyena atimātra-bhaktyā ca mām eva prapannāya te — to you, who have taken refuge in me alone with friendship and boundless devotion; saparikaraḥ savistaram uktaḥ — it has been told with all its parts and in detail. Mad-anyena kena api jñātuṃ vaktuṃ vā na śakyam — no one other than me can know it or tell it; vedāntoditam uttamaṃ rahasyaṃ jñānam — the supreme secret knowledge taught in the Vedanta.