瑜伽師地論略纂 2.119

2.119

The Four Great Heavenly Kings are named after each of their rulers. By what are the Thirty-Three Gods named? On each of the four sides of Mount Meru there are eight heavens, and Śakra resides in the center; hence the thirty-three lords and subjects are collectively designated. The Yāma Heaven is named "Time Division" because they enjoy pleasure according to time divisions. The Tuṣita Heaven is named "Contentment" because they are content in their enjoyment of pleasure. The remaining two are explained below.