व्यासप्रसादाच्छ्रुतवान् एतद् गुह्यमहं परम्योगं योगेश्वरात् कृष्णात् साक्षात् कथयतः स्वयम्
In plain words
By the grace of Vyasa, I heard this supreme and secret yoga directly from Krishna, the Lord of Yoga, Himself declaring it.
Word for word
By the grace of Vyāsa I have heard this secret, supreme yoga directly from Kṛṣṇa, the Lord of yoga, as He Himself told it.
The commentators
Bhagavadgītābhāṣyam
तं च इमम् —
व्यासप्रसादात् ततः दिव्यचक्षुर्लाभात् श्रुतवान् इमं संवादं गुह्यतमं परं योगम् , योगार्थत्वात् ग्रन्थोऽपि योगः, संवादम् इमं योगमेव वा योगेश्वरात् कृष्णात् साक्षात् कथयतः स्वयम् , न परम्परया ॥ ७५ ॥
In plain words
And this very one, too —
Vyāsa's grace gave me divine sight, and with that sight I heard this conversation: the most guarded of secrets, the supreme yoga. Since yoga is what the text is about, the text is called yoga as well; or say instead that this conversation simply is yoga. And I heard it from Kṛṣṇa, the Lord of yoga, directly — from his own mouth, as he spoke it — not handed down to me through anyone else.
Close to the Sanskrit
And him, this very one —
By the grace of Vyāsa, and thence from the obtaining of divine sight, [I] have heard this dialogue, most secret, the supreme yoga. Because it has yoga for its subject-matter, the text too is called yoga; or else this dialogue is yoga itself. [Heard] from Kṛṣṇa, the Lord of yoga, directly, from him telling it in his own person — not through a line of transmission.