In Bhagavad Gita 18th chapter, it is explained that for one who explains the supreme secret to devotees devotional service is guaranteed and will go back to Godhead.
Bg 18.66 — Abandon all varieties of religion and just surrender unto Me. I shall deliver you from all sinful reactions. Do not fear.
Bg 18.67 — This conﬁdential knowledge may never be explained to those who are not austere, or devoted, or engaged in devotional service, nor to one who is envious of Me.
Bg 18.68 — For one who explains this supreme secret to the devotees, pure devotional service is guaranteed, and at the end he will come back to Me.
Bg 18.69 — There is no servant in this world more dear to Me than he, nor will there ever be one more dear.
Does the "supreme secret" refer to the entire Bhagavad Gita or the shloka 18.66?
How can I get qualified to explain the supreme secret and how can I find devotees, who would be willing to listen to me?