Chapter 18, Verse 68
Part of 18: Mokṣha Sanyās Yog — मोक्षसंन्यासयोगय इमं परमं गुह्यं मद्भक्तेष्वभिधास्यति।भक्ितं मयि परां कृत्वा मामेवैष्यत्यसंशयः॥
ya idaṁ paramaṁ guhyaṁ mad-bhakteṣhv abhidhāsyati bhaktiṁ mayi parāṁ kṛitvā mām evaiṣhyaty asanśhayaḥ
He who, with supreme devotion to Me, teaches this supreme secret to My devotees, shall undoubtedly come to Me.
This supreme secret The teachings of the Gita as taught above in the form of a dialogue between Lord Krishna and Arjuna. Why is it called a supreme secret Because it helps one to attain immortality or freedom from the whell of birth and death. He alone, who has devotion, is alified to receive the teachings of the Gita. Teach with the faith that he is thus doing service to the Lord, the Supreme Teacher. Doubtless may also mean freedom from doubts.