स एवायं मया तेऽद्य योगः प्रोक्तः पुरातनः ।भक्तोऽसि मे सखा चेति रहस्यं ह्येतदुत्तमम् ॥
sa evāyaṃ mayā te'dya yogaḥ proktaḥ purātanaḥ |bhakto'si me sakhā ceti rahasyaṃ hyetaduttamam ||
That same ancient yoga I have taught you today, because you are my devotee and my friend; for this is a supreme secret.
Explanation
Krishna has just said that this yoga (the discipline of selfless action joined with knowledge) was lost over time. Here he explains why he is restoring it to Arjuna now: Arjuna is his devotee (bhakta) and friend (sakhā). He calls it a supreme secret (rahasya), meaning a teaching that is deep and meant for those ready to receive it.