The 22 levels from earth to sky refer to the development of the Wish for Budhahood (Bodhichitta), from the initial intention in a baby Bodhisattva to the full Bodhichitta in the mind of a Buddha. This list of 22 comes from the Ornament of Realizations (Abhisamayalankara) by Arya Asanga which is one of the Five Great Books of Maitreya—The Future Buddha. They were taught by Maitreya to Arya Asanga in Maitreya’s heaven and then he brought them back to this world.
Geshe Michael uses two commentaries for this teaching, one by the First Panchen Lama, Lobsang Chukyi Gyeltsen and the other by Je Tsongkapa called the Golden Garland.
This was a teaching requested by one of Geshe Michael’s students and taught in a small private class in his hotel room in the wee hours of April 22, 2016 in Beijing. It’s taught in English with Chinese interpretation.