4:3  

स एवायं मया तेऽद्य योगः प्रोक्तः पुरातनः ।
भक्तोऽसि मे सखा चेति रहस्यं ह्येतदुत्तमम् ॥४-३॥

sa ewaayaM mayaa te'dya yogaH proktaH puraatanaH ।

bhakto'si me sakhaa cheti rahasyaM hyetaduttamam ॥४-३॥

Source: Automatic ITRANS Transliteration

This same yoga, by me to you today is articulated, ancient.
Since you are my devotee and friend, then this supreme mystery.

This same ancient yoga, the supreme mystery, is articulated by me to you today, because you are my devotee and friend.

Source: Milind S. Pandit

Today I have described the same ancient science to you, because you are my sincere devotee and friend. Karma-yoga is a supreme secret indeed.

Source: The Bhagavad-Gita: The Sacred Song

That very ancient science of the relationship with the Supreme is today told by Me to you because you are My devotee as well as My friend; therefore you can understand the transcendental mystery of this science.

Source: Bhagavad Gita As It Is