18.66 is the verse most people know. Set every duty down. Take refuge in me alone. I will free you from every sin. Do not grieve. It is verse 688 of 700, and many readers treat it as the last word.
It isn’t. Kṛṣṇa keeps talking.
In the verses that follow, he turns from Arjuna to everyone who will ever pass this teaching on. Whoever shares this highest mystery with those who love me, he says at 18.68, will come to me. At 18.69 he goes further: no one on earth does anything dearer to me than this, and no one will be dearer to me.
The Gītā’s most famous promise is made to the student. The one after it is made to whoever tells the next person.
His last teaching was about passing it on.
Going deeper
18.66 is the verse most people know, and it is not where the Gītā ends. 18.67 follows with a limit: this should never be told to one who is not austere, not a devotee, not willing to listen, or who speaks ill of Kṛṣṇa. Then 18.68 turns to the person who passes the teaching on: whoever proclaims this supreme secret among his devotees acquires supreme devotion and will come to him, with no doubt. 18.69 goes further: no one among people does him dearer service, and no one on earth will be dearer to him. 18.70 and 18.71 extend the promise to those who study the dialogue and those who listen with faith. 18.72 is Kṛṣṇa's final question to Arjuna. The best known promise is made to the student, and the ones after it to whoever hands the teaching on. The passage is in chapter 18, and what the Gītā says about devotion gathers related verses.